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Synthesis 2015; 47(24): 3823-3845
DOI: 10.1055/s-0035-1560346
review
© Georg Thieme Verlag Stuttgart · New York

C–H Bond Transformations Leading to the Synthesis of Organic Functional Materials

Yoichiro Kuninobu*
a   Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan   Email: kuninobu@mol.f.u-tokyo.ac.jp
b   CREST, Japan Science and Technology Agency (JST), 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
,
Shunsuke Sueki
a   Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan   Email: kuninobu@mol.f.u-tokyo.ac.jp
b   CREST, Japan Science and Technology Agency (JST), 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
› Author Affiliations
Further Information

Publication History

Received: 23 July 2015

Accepted after revision: 10 August 2015

Publication Date:
24 September 2015 (online)

 
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Abstract

In this review, transition-metal-catalyzed or -mediated C–H transformations leading to the synthesis of organic functional materials, such as oligomers, polymers, and π-conjugated molecules, are summarized.

1 Introduction

2 Oligomers and Polymers

2.1 Synthesis of Oligomers and Polymers

2.2 Chemical Modification of Polymers

3 π-Conjugated Molecules

3.1 Indenes and Fluorenes

3.2 Acenes

3.3 Triphenylenes

3.4 Chemical Modification of Perylene Diimides

3.5 Nanographenes

3.6 Condensed Polycyclic π-Conjugated Molecules with Five-Membered Heteroaromatic Rings

3.7 π-Conjugated Molecules with Nitrogen-Containing Six-Membered Heteroaromatics

3.8 Porphyrins

3.9 Miscellaneous (π-Conjugated Molecules)

4 Miscellaneous (Excluding Polymers and π-Conjugated Molecules)

5 Outlook and Conclusions


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Key words

catalyst - C–H activation - C–H functionalization - π-conjugated molecule - π-conjugation - functional material - oligomer - polymer

Biographical Sketches

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Yoichiro Kuninobu is an Associate Professor and ERATO project group leader at the University of Tokyo in Japan. He was born in Japan (Kanagawa) in 1976. He received his B.S. and Ph.D. degrees from the University of Tokyo­ in 1999 and 2004, respectively, under the supervision of Professor Eiichi Nakamura. He was appointed to Assistant Professor at Okayama University in 2003 and worked with Professor Kazuhiko Takai. Then, he moved to the University of Tokyo and is now working with Prof. Motomu Kanai in his current position. He has been recognized with a number of awards: Meiji Seika Award in Synthetic Organic Chemistry, Japan (2006), Science and Technology Award in Okayama Foundation of Science and Technology (2007), OMCOS 14 Poster Award (2007), Incentive Award in Tyugoku-Shikoku Branch of the Society of Synthetic Organic Chemistry, Japan (2007), 22th Lectureship award for young chemists at the 88th annual meeting of the Chemical Society of Japan (2008), BCSJ Award (2008), Incentive Award for Young Top Researcher in Okayama University (2009), Banyu Chemist Award (BCA 2010), The Chemical Society of Japan Award for Young Chemists (2011), Thieme Chemistry Journal Award 2012 (2011), The Young Scientists’ Prize, The Commendation for Science and Technology by the Minister of Education, Culture, Sports, Science and Technology (2012), and JST-ERATO Lectureship Award (2015). His research interests are related to the development of novel and highly efficient synthetic organic reactions and the creation of novel organic functional materials.

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Shunsuke Sueki is a CREST postdoctoral researcher at the University of Tokyo in Japan. He was born in Japan (Hyogo) in 1983. He received his B.E. and Ph.D. degrees from Waseda University in 2006 and 2010, respectively, under the supervision of Professor Isao Shimizu. He was a research associate in the group of Prof. Shimizu at Waseda University from 2010–2012, and he moved to his current position at the University of Tokyo in 2012 and is now working with Associate Professor Yoichiro Kuninobu. He has been recognized with the following awards: Shimazaki Kazuo Award (Waseda University, 2006), CSJ Kanto Branch 2nd Student Presentation Award (The Chemical Society of Japan, 2008), Mizuno Award (Waseda University, 2010), and CSJ Presentation Award 2013 (The Chemical Society of Japan, 2013). His research interests are related to the development of new synthetic organic reactions using transition-metal catalysts.

1

Introduction

Oligomers, polymers, and π-conjugated molecules are important because such molecules have potentials as organic functional materials. Therefore, many reactions for the synthesis of such molecules have been developed to date. For example, addition polymerization, polycondensation, and addition condensation are efficient methods for the synthesis of oligomers and polymers, and cross-coupling reactions and annulation/aromatization are the standard methods for the construction of π-conjugated systems. However, such reactions require multistep prefunctionalization and generate large amounts of waste, hence, they are not completely satisfactory. Therefore, the development of efficient and practical methods is important from the viewpoint of shortening reaction times, lowering costs, and decreasing byproduct formation, among others.

Researchers have recently focused on transition-metal-catalyzed direct C–H bond transformations, and developed many types of reaction.[1] In the fields of organic functional materials, there is also a growing tendency to synthesize organic functional molecules by direct C–H bond transformation and such reactions are undergoing further development. In this review, we highlighted reactions directed toward the synthesis of organic functional molecules and reactions that could be used for the synthesis of such molecules.

In section 2, we introduce the synthesis of oligomers and polymers by transition-metal-catalyzed C–H bond transformation. Such oligomer and polymer skeletons are obtained by C–H insertion of unsaturated molecules and cross-coupling reactions between C–H and C–halogen bonds of aromatic and heteroaromatic compounds. Polymer chains can be modified by C–H functionalization.

In section 3, C–H bond transformations that could be used for the synthesis of π-conjugated molecules are described. Section 3 is subdivided according to the type of core structure, such as indenes, fluorenes, acenes, triphenylenes, perylenes, nanographenes, condensed polycyclic π-conjugated molecules with five-membered heteroaromatic rings, π-conjugated molecules with nitrogen-containing six-membered heteroaromatic rings, and porphyrins.

The synthesis and modification of other organic functional materials by C–H bond transformations, such as the functionalization of metal organic frameworks (MOF) and liquid crystals, are summarized in section 4.

In addition to this review, several other useful reviews are available.[2]


# 2

Oligomers and Polymers

2.1

Synthesis of Oligomers and Polymers

Polymers play an important role in our lives, and various functional polymers have been created.[3] Typical polymerizations, such as addition and condensation polymerizations, are promising methods for the preparation of well-defined polymers. Transition-metal-catalyzed polymerizations are also well established.[4] In this section, the synthesis of polymers by C–H bond transformations are discussed.

2.1.1

By C–H Insertion

Weber and co-workers reported the ruthenium-catalyzed regioselective step-growth copolymerization of acetophenones and α,ω-dienes (Scheme [1]).[5] The Murai reaction is key to this polymerization, and it is necessary to treat the ruthenium catalyst [RuH2(CO)(PPh3)3] with a stoichiometric amount of an alkene, such as styrene, to generate the active catalyst.

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Scheme 1 Ruthenium-catalyzed regioselective step-growth copolymerization of acetophenones and α,ω-dienes

Kuninobu and co-workers reported the rhenium-catalyzed synthesis of 3-iminoisoindolin-1-ones via insertion of isocyanates into the C–H bond of aromatic carboximidates (Scheme [2]).[6] They also succeeded in the synthesis of polyimides that are highly soluble into organic solvents, such as toluene, tetrahydrofuran, dichloromethane, and chloroform.

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Scheme 2 Rhenium-catalyzed synthesis of polyimide derivatives via insertion of diisocyanates into the C–H bond of aromatic dicarboximidates
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Scheme 3 Palladium-catalyzed synthesis of oligothiophenes by C–H arylation with 2-bromo-3-hexylthiophene followed by halogen exchange
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Scheme 4 Rhodium-catalyzed synthesis of poly(pyrazolylnaphthalene)s

# 2.1.2

By Cross-Coupling Reactions

C–H Cross-coupling reactions, particularly C–H/C–halogen cross-coupling reactions, have been applied to the synthesis of oligomers and polymers. Mori and co-workers reported the palladium-catalyzed synthesis of oligothiophenes by C–H arylation with 2-bromo-3-hexylthiophene followed by halogen exchange (Scheme [3]).[7] This modular-type synthesis provides oligothiophenes in a good head-to-tail manner.

In 2013, Tang and co-workers reported the rhodium-catalyzed synthesis of poly(pyrazolylnaphthalene)s in the presence of a copper oxidant (Scheme [4]).[8] The synthesized polymers have high molecular weights and they are thermally stable with high reflective indices. As explosives, such as picric acid, quench the fluorescence of the polymer carrying tetraphenylethene units, its use as a sensitive chemosensor for explosives was discussed.

In 1999, Lemaire and co-workers reported the palladium-catalyzed polymerization of 3-alkyl-2-iodothiophenes using a cross-coupling reaction in good yields and head-to-tail selectivity, but the molecular weights of the polymers were not high (Scheme [5]).[9]

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Scheme 5 Palladium-catalyzed polymerization of 3-alkyl-2-iodothiophenes using a cross-coupling reaction

Takita, Ozawa, and co-workers reported the polymerization of 2-bromo-3-hexylthiophenes using the Herrmann’s catalyst/tris[2-(dimethylamino)phenyl]phosphine system (Scheme [6]).[10] [11] The synthesized polythiophenes had excellent yields with good head-to-tail selectivity and high molecular weights.

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Scheme 6 Polymerization of 2-bromo-3-hexylthiophenes using the Herrmann’s catalyst/tris[2-(dimethylamino)phenyl]phosphine system

Kanbara and co-workers developed a palladium/phosphine-catalyzed copolymerization between N-alkyl-3,6-dibromocarbazoles and tetrafluorobenzene under basic conditions (Scheme [7]).[12] [13] Although the molecular weights of the polymers were relatively low, blue fluorescence was observed in chloroform and 1,1,2,2-tetrachloroethane solutions.

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Scheme 7 Palladium/phosphine-catalyzed copolymerization between dibromocarbazoles and tetrafluorobenzene

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# 2.2

Chemical Modification of Polymers

C–H Transformations are also strong and efficient methods for the introduction of various functional groups into polymers. Hartwig, Hillmyer, and co-workers reported the rhodium-catalyzed C–H borylation of polyethylethylenes; subsequent hydrolysis gave polymers containing hydroxyl groups (Scheme [8]).[14] It is notable that this is the first example of a late-stage C–H functionalization of polymers.

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Scheme 8 Rhodium-catalyzed C–H borylation of polyethylethylenes

Noh, Bae, Lee, and co-workers reported the iridium-catalyzed C–H borylation of polystyrenes in moderate to good yields (Scheme [9]).[15] [16] The efficiency of C–H borylation was affected by the tacticity of polystyrenes.

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Scheme 9 Iridium-catalyzed C–H borylation of polystyrenes

In 2011, Tsurugi, Mashima, and co-workers synthesized an yttrium ene–diamido complex that reacted with 2,4,6-collidine to give an yttrium alkyl complex via C–H activation. This complex showed a catalytic activity for the polymerization of 2-vinylpyridines to afford poly(2-vinylpyridine)s in excellent yields and polydispersity (Scheme [10]).[17]

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Scheme 10 Polymerization of 2-vinylpyridines using an yttrium ene–diamido complex

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# 3

π-Conjugated Molecules

3.1

Indenes and Fluorenes

Fluorenes are an important class of compounds that are utilized in functional materials, such as components for organic field effect transistor (OFET) devices[18] and biosensors.[19] Satoh, Miura, and co-workers reported a rhodium-catalyzed intramolecular C–H/C–H coupling reaction that provided aminofluorenes in excellent yields (Scheme [11]).[20] A rhodium-catalyzed synthesis of substituted fluorenes using 2,2-diphenylalkanoic acids was also developed.

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Scheme 11 Aminofluorenes by a rhodium-catalyzed intramolecular C–H/C–H coupling reaction

In 2013, Satoh, Miura, and co-workers also developed an iridium-catalyzed synthesis of fluorenols via C–H activation. The hydroxy group was retained in the products (Scheme [12]).[21]

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Scheme 12 Iridium-catalyzed synthesis of fluorenols via C–H activation

Indene and silylindene scaffolds are recognized not only in the structures of natural products[22] and drugs,[23] but also in ligands for olefin polymerization.[24] In 2015, Kuninobu and co-worker reported the rhodium-catalyzed synthesis of multisubstituted silylindenes using hydrosilanes and di­arylacetylenes (Scheme [13]).[25] The silylindenes were stable in air and exhibited blue fluorescence.

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Scheme 13 Rhodium-catalyzed synthesis of multisubstituted silylindenes using hydrosilanes and diarylacetylenes

Glorius and co-workers reported the rhodium-catalyzed synthesis of indenols from aryl ketones and internal alkynes via C–H bond activation. Fulvenes were also obtained by in situ dehydration of indenols (Scheme [14]).[26]

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Scheme 14 Rhodium-catalyzed synthesis of indenols and fulvenes via C–H bond activation

# 3.2

Acenes

Acenes have fused benzene rings and show semiconducting properties. Acenes, such as pentacenes and rubrenes, are used in the active layers of organic field effect transistors (OFETs) with high hole mobilities.[27] Many acene derivatives have been prepared to test their potential as high performance organic electronics. Therefore, it is important to develop efficient methods for the synthesis of a wide variety of acenes.

3.2.1

Construction of Acene Skeletons

3.2.1.1 Construction of Acene Skeletons by C–H Insertion

The following reactions relate to the construction of acene skeletons by annulation reactions between arenes and internal alkynes.

Satoh, Miura, and co-workers reported the rhodium-catalyzed synthesis of naphthyl- and anthryl-azoles from 2-phenylazoles and internal alkynes by oxidative annulation by multiple C–H bond activation (Scheme [15]);[28] some of the products showed blue fluorescence in the solid state.

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Scheme 15 Rhodium-catalyzed synthesis of anthrylazoles from 2-phenylazoles and internal alkynes

Wu and co-workers reported the palladium-catalyzed synthesis of highly substituted naphthalene derivatives from arenes and internal alkynes (Scheme [16]).[29] Single crystal X-ray structure analysis showed that the naphthalene derivatives have a twisted naphthalene core. It was concluded that the twisted structures were induced by the overcrowded substituents and the CH3–π interaction.

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Scheme 16 Palladium-catalyzed synthesis of highly substituted naphthalene derivatives from arenes and internal alkynes

Cramer and co-worker reported the rhodium-catalyzed synthesis of highly substituted arenes by formal oxidative [2+2+2]-cycloaddition reactions between one equivalent of arene and two equivalents of internal alkyne (Scheme [17]).[30] The products are highly soluble in organic solvents; photophysical properties were also reported.

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Scheme 17 Rhodium-catalyzed synthesis of highly substituted arenes by formal oxidative [2+2+2]-cycloaddition reactions

Miura and co-workers reported the iridium-catalyzed synthesis of phenanthrene derivatives from 2-arylbenzoyl chlorides and internal alkynes (Scheme [18]).[31] In this reaction, the addition of a base was not necessary even though HCl was formed. Deuterium-labeling experiments showed that the rate-determining step did not involve C–H bond cleavage.

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Scheme 18 Iridium-catalyzed synthesis of phenanthrene derivatives from 2-arylbenzoyl chlorides and internal alkynes

The following two reactions involve the construction of dibenzo[a,e]pentalenes. Segawa, Itami, and co-worker reported the palladium-catalyzed oxidative synthesis of dibenzo[a,e]pentalenes by annulative dimerization of di­arylacetylenes (Scheme [19]).[32] UV-vis absorption spectra and DFT calculations indicated a strong substituent effect on the energy levels of the HOMO and HOMO-1.

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Scheme 19 Palladium-catalyzed oxidative synthesis of dibenzo[a,e]pentalenes by annulative dimerization of diarylacetylenes

Jin and co-workers reported the palladium-catalyzed cascade crossover annulation between o-alkynylaryl halides and diarylacetylenes (Scheme [20]).[33] This reaction provided multisubstituted dibenzo[a,e]pentalenes with different substituents; UV-vis absorption spectra and DFT calculations were also reported.

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Scheme 20 Palladium-catalyzed cascade crossover annulation between o-alkynylaryl halides and diarylacetylenes

The following two reactions are the construction of arenes via C–H insertion and successive cyclization. Kuninobu­, Takai, and co-workers reported the rhenium-catalyzed synthesis of isobenzofurans from aromatic imines and aldehydes via C–H bond activation.[34] Using this reaction, they successfully synthesized 5- and 16-substituted unsymmetric pentacene derivatives (Scheme [21]).[35] A variety of functional groups can be introduced into the pentacene skeleton using this route.

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Scheme 21 Rhenium-catalyzed synthesis of isobenzofurans from aromatic imines and aldehydes via C–H bond activation

Darses and co-workers reported the ruthenium-catalyzed insertion of styrenes into the ortho-C–H bond of aromatic aldimines;[36] this reaction gave aromatic aldimines with a linear alkyl chain. In contrast, Yoshikai and co-worker reported the cobalt-catalyzed synthesis of aromatic aldimines with a branched alkyl chain by the ortho-selective insertion of a styrene (Scheme [22]).[37] The products were converted into polyaromatic hydrocarbons using the indium-catalyzed construction of aromatic rings reported by Kuninobu­, Takai, and co-workers.[38]

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Scheme 22 Cobalt-catalyzed synthesis of aromatic aldimines with a branched alkyl chain by ortho-selective insertion of styrenes

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3.2.1.2 Construction of Acene Skeletons by C–H Coupling Reactions

Nishihara and co-workers reported the palladium-catalyzed synthesis of [6]phenacenes by two Suzuki–Miyaura cross-coupling reactions and successive intramolecular C–H/C–Cl coupling reactions (Scheme [23]).[39] The physicochemical properties of the products were investigated by UV-vis and fluorescence spectroscopy, and cyclic voltammetry.

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Scheme 23 Palladium-catalyzed synthesis of [6]phenacenes by two Suzuki–Miyaura cross-coupling reactions and successive intramolecular C–H/C–Cl coupling reactions

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# 3.2.2

Chemical Modification of Acene Skeletons

Oi, Inoue, and co-workers reported the palladium-catalyzed oxidative C–H arylation of arenes using aryltin reagents (Scheme [24]);[40] a similar reaction was achieved using arylsilicon reagents.[41] In these reactions, copper(II) chloride was an activator for the palladium intermediate as well as an oxidant.

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Scheme 24 Palladium-catalyzed C–H arylation of arenes using aryltin reagents

Kakiuchi and co-workers reported the ruthenium-catalyzed synthesis of multi-arylated acenes by ruthenium-catalyzed­ C–H arylation and successive transformations (Scheme [25]).[42] Single-crystal X-ray structure analysis showed that the anthracene skeleton of the product in Scheme [25] was twisted by the steric repulsion of the aryl groups.

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Scheme 25 Ruthenium-catalyzed synthesis of multi-arylated acenes by ruthenium-catalyzed C–H arylation and successive transformations

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# 3.3

Triphenylenes

Polycyclic aromatic hydrocarbons (PAHs) have unique electronic and photophysical properties for organic devices.[43] Triphenylenes are particularly important compounds for organic light-emitting diodes and as discotic liquid crystal materials, but the construction of the triphenylene scaffolds are still challenging in terms of regioselectivity. Nishihara­ and co-workers reported that the reaction between 2-iodobiphenyls and a 2-bromobenzyl alcohol in the presence of a palladium catalyst and an electron-deficient phosphine ligand provided substituted triphenylenes in good yields (Scheme [26]).[44] This reaction proceeded via β-carbon elimination to release acetone.

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Scheme 26 Palladium-catalyzed synthesis of substituted triphenylenes between 2-iodobiphenyls and a 2-bromobenzyl alcohol

In 2015, Yorimitsu, Osuka, and co-worker reported an efficient palladium-catalyzed synthesis of triphenylenes using teraryl sulfonium salts (Scheme [27]).[45] The key point in this process was the decrease in Lewis basicity of the sulfur atom that permitted the desired cross-coupling reaction; a similar reaction started from sulfoxides.

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Scheme 27 Palladium-catalyzed synthesis of triphenylenes using teraryl sulfonium salts

In 2015, Glorius and co-workers reported the palladium-catalyzed C–H arylation of polycyclic aromatic hydrocarbons, such as naphthalene, triphenylene, and related arenes (Scheme [28]).[46] It was proposed that palladium nanoparticles, which were generated in situ, were the active catalyst based on mechanistic studies.

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Scheme 28 Palladium-catalyzed C–H arylation of triphenylene

# 3.4

Chemical Modification of Perylene Diimides

Perylene diimides play an important role in material sciences, such as n-channel semiconductors,[47] pigments,[48] protein-tagging,[49] and organic solar cells.[50] Several methods for the derivatization of perylene diimides using C–H bond functionalization have been reported. In 2009, Kim, Shinokubo­, Osaka, and co-workers reported that ruthenium-catalyzed C–H arylation provided tetraarylated perylene diimides in the 2,5,8,11-positions in good yields with perfect regioselectivity (Scheme [29]).[51a] The functionalized perylene diimides exhibited blue fluorescence in good quantum yields. The ruthenium-catalyzed C–H alkyl­ation of perylene diimides has also been reported.[51b]

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Scheme 29 Ruthenium-catalyzed C–H arylation reaction to provide tetraarylated perylene diimides

Wang and co-workers reported the palladium-catalyzed meta-selective C–H alkylation of perylene diimides (Scheme [30]).[52] The alkylated perylene diimides showed blue fluorescence (539–542 nm) with small Stokes shifts. Cyclic voltammetry of the perylene diimides exhibited reversible reduction waves.

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Scheme 30 Palladium-catalyzed C–H alkylation of perylene diimides

The C–H phosphonethylation of perylene diimides using the Murai reaction was developed by Müllen and co-workers (Scheme [31]).[53] The perylene diimides were hydrolyzed to give water-soluble perylene diimides that showed blue fluorescence; they were applied to fluorescence imaging of HeLa cells.

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Scheme 31 Synthesis of water-soluble perylene diimides by palladium-catalyzed C–H phosphonethylation

Shinokubo and co-workers reported the iridium/electron-deficient phosphine catalyzed C–H borylation of perylene diimides (Scheme [32]).[54] The borylated perylene diimides underwent the Suzuki–Miyaura cross-coupling reaction to give tetraarylated perylene diimides. Oxidation with hydroxylamine under basic conditions afforded tetrahydroxyperylene diimides.

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Scheme 32 Iridium-catalyzed C–H borylation of perylene diimides

Marder and co-workers reported ruthenium-catalyzed C–H borylation and subsequent bromination to give brominated perylene diimides (Scheme [33]).[55] The brominated perylene diimides underwent Stille coupling to provide perylene diimide–donor–perylene diimide triads that were shown to function as solution-processable electron-transport materials in field-effect transistors.

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Scheme 33 Ruthenium-catalyzed C–H borylation, bromination, and Stille coupling of perylene diimides

Pantoş, Lewis, and co-workers reported the iridium-catalyzed C–H borylation of naphthalenediimides (Scheme [34]).[56] Borylated naphthalenediimides were converted into arylated naphthalenediimides via Suzuki–Miyaura cross coupling.

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Scheme 34 Iridium-catalyzed C–H borylation of naphthalenediimides

# 3.5

Nanographenes

Nanographenes are a class of graphenes that have received much attention because of their unique electronic properties.[57] Graphenes were first prepared by chemical vapor deposition (CVD),[58] but it is difficult to prepare derivatized nanographenes by this method. Therefore, methods for the chemical synthesis of nanographenes are required for their development in materials science.[59] In 2005, Marder and co-workers developed a selective C–H borylation of polycyclic aromatic hydrocarbons, such as naphthalene, pyrene, and perylene (Scheme [35]).[60] [61] Although this method provided a mixture of regioisomers in the case of naphthalene and pyrene, a highly symmetric tetraborylated perylene was obtained as a single product in good yield.

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Scheme 35 Iridium-catalyzed selective C–H borylation of polycyclic aromatic hydrocarbons

Scott and co-worker developed the iridium-catalyzed C–H polyborylation of corannulene in moderate to good yields (Scheme [36]).[62] This reaction required the use of excess borylation reagent and proceeded by deborylation/reborylation and reposition of boryl groups.

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Scheme 36 Iridium-catalyzed C–H polyborylation of corannulene

Shinokubo and co-workers developed the iridium-catalyzed C–H borylation of hexabenzocoronenes; subsequent hydrolysis gave trihydroxy-substituted hexabenzocoronenes (Scheme [37]).[63] The corresponding hexabenzocoronenes showed blue fluorescence and they have potential as materials with large two-photon absorption cross-section values.[63b]

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Scheme 37 Iridium-catalyzed C–H borylation of hexabenzocoronene
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Scheme 38 Palladium-catalyzed C–H arylation of pyrenes

Itami and co-workers reported the direct C–H arylation of polycyclic aromatic hydrocarbons, for example, between pyrenes and arylboroxins to afford hexabenzotetracenes in moderate yields with good regioselectivity in the K-region (the convex armchair edge of polycyclic aromatic hydrocarbons) (Scheme [38]).[64] In the course of the study, it was found that a combination of a palladium catalyst and o-chloranil oxidant is the best reaction system for the arylation. They also applied similar reaction conditions to the direct C–H arylation of other polycyclic aromatic hydrocarbons;[65] notable is the synthesis of decakis(4-chlorophenyl)corannulene via C–H arylation in satisfactory yield (Scheme [39]).

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Scheme 39 Synthesis of decakis(4-chlorophenyl)corannulene via C–H arylation
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Scheme 40 Synthesis of warped nanographene via C–H borylation of corannulene

Using previously developed techniques, Itami and co-workers then also applied C–H functionalization to corannulene to develop a new synthetic route to access a nano­graphene sheet (Scheme [40]).[66] A pentaborylated corannulene was converted into a biphenyl-ligated corannulene, which was cyclized under oxidative conditions to afford a warped nanographene.

In 2015, Itami and co-workers reported a one-shot K-region­-selective annulative π-extension for the synthesis of graphenes and nanographenes via C–H bond transformations using a palladium catalyst/o-chloranil system (Scheme [41]).[67] This method was applied to various types of functionalized nanographenes.

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Scheme 41 Palladium-catalyzed K-region-selective annulative π-extension for the synthesis of graphenes and nanographenes via C–H bond transformations

# 3.6

Condensed Polycyclic π-Conjugated Molecules with Five-Membered Heteroaromatic Rings

Ladder-type π-conjugated molecules containing heteroatoms have received much attention because of their usefulness as organic functional materials, such as organic light-emitting diodes, organic thin film transistors, and photovoltaic devices.[68] Several synthetic methods have been developed for the construction of suitable heterocycles, and the most popular method involves coupling reactions between dilithiated biaryls and heteroatom compounds bearing two or more halogen atoms.[69] Another method utilizes intramolecular reductive double cyclization with an alkyne moiety.[70] More attractive synthetic methods for the construction of heteroatom-containing ladder-type π-conjugated molecules utilize direct C–H bond transformations.

3.6.1

Carbon–Heteroatom Bond-Formation Reactions

Kuninobu, Takai, and co-workers reported the rhodium-catalyzed synthesis of silafluorene (dibenzosilole) derivatives from biphenyl(hydro)silanes (Scheme [42]).[71] This highly efficient reaction proceeded by both Si–H and C–H bond activation with the formation of only hydrogen as a side product. A ladder-type bis-silicon-bridged p-terphenyl was also synthesized using this method.

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Scheme 42 Rhodium-catalyzed synthesis of silafluorene derivatives from biphenyl(hydro)silanes

Kuninobu, Takai, and co-workers also applied this reaction to the synthesis of chiral spirosilabifluorene derivatives (Scheme [43]).[72] Treatment of bis(biphenyl)silanes with a catalytic amount of a rhodium complex {RhCl(PPh3)3, or a mixture of [RhCl(cod)]2 and rac-BINAP} gave spirosilabifluorenes bearing a quaternary silicon atom. Using a rhodium catalyst with a chiral phosphine ligand {[RhCl(cod)]2, (R)-BINAP} resulted in asymmetric dehydrogenative cyclization proceeding twice to give chiral spirosilabifluorene derivatives in good yields and with good enantioselectivity.

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Scheme 43 Asymmetric synthesis of spirosilabifluorenes

Kuninobu, Takai, and co-worker also reported the synthesis of phosphafluorene (dibenzophosphole) oxides from secondary biphenyl(hydro)phosphine oxides by dehydrogenation via P–H and C–H bond cleavage in the presence of a catalytic amount of palladium(II) acetate (Scheme [44]).[73] By using this reaction, a ladder-type dibenzophosphole oxide was also synthesized by double intramolecular dehydrogenative cyclization.

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Scheme 44 Palladium-catalyzed synthesis of phosphafluorene (dibenzophosphole) oxides

Kuninobu, Takai, and co-workers achieved ortho-selective C–H borylation using a Lewis acid–base interaction (Scheme [45]).[74] Treatment of 2-phenylpyridine (or its derivatives) with 9-borabicyclo[3.3.1]nonane (9-BBN) in the presence of a palladium catalyst resulted in regioselective C–H borylation at the ortho-position of the aromatic compound. In this reaction, the Lewis acid–base interaction between the boron and nitrogen atoms is important in the control of the regioselectivity. In addition, this reaction proceeded even at room temperature. The products are borafluorene (dibenzoborole) equivalents and show blue fluorescence.

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Scheme 45 Palladium-catalyzed regioselective C–H borylation of 2-phenylpyridines

A similar concept was used in the synthesis of silafluorene equivalents. Kuninobu, Kanai, and co-worker reported the iridium-catalyzed direct and ortho-selective C–H silylation of 2-phenylpyridines (Scheme [46]).[75] The regioselectivity was controlled by the Lewis acid–base interaction between the Lewis acidic silicon atom of the fluorinated hydrosilane and the Lewis basic nitrogen atom of the 2-phenylpyridine.

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Scheme 46 Iridium-catalyzed direct and ortho-selective C–H silylation of 2-phenylpyridines

The silafluorene equivalent shown in Scheme [46] was synthesized by another method. Kuninobu, Kanai, and co-workers succeeded in the synthesis of silafluorene equivalents by the treatment of 2-phenylpyridines with an amino(1,3,2-dioxaborolan-2-yl)diphenylsilane in good to excellent yields under palladium catalysis (Scheme [47]).[76] This reaction is the first example of C–H fluorosilylation. Single-crystal X-ray structure analysis showed the Lewis acid–base interaction between the silicon and nitrogen atoms. Interestingly, the fluorosilylated products showed stronger fluorescence than the corresponding silafluorene derivative.

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Scheme 47 Palladium-catalyzed C–H fluorosilylation of 2-phenylpyridines

Yoshikai and co-worker reported the palladium-catalyzed synthesis of dibenzofuran derivatives from 2-arylphenols by an intramolecular oxidative C–H/O–H coupling reaction (Scheme [48]).[77] Kinetic isotope effect experiments indicated that C–H bond cleavage is the rate-determining step of the reaction.

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Scheme 48 Palladium-catalyzed synthesis of dibenzofuran derivatives from 2-arylphenols by an intramolecular oxidative C–H/O–H coupling reaction

Deng, Li, and co-workers reported the palladium-catalyzed synthesis of benzothieno[2,3-b]indoles from indole derivatives, cyclohexanone, and sulfur powder (Scheme [49]).[78] This reaction proceeded via dehydrative–dehydrogenative double C–H sulfuration.

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Scheme 49 Palladium-catalyzed synthesis of benzothieno[2,3-b]indoles via dehydrative–dehydrogenative double C–H sulfuration

# 3.6.2

Carbon–Carbon Bond-Formation Reactions

Another possible strategy for the synthesis of condensed polycyclic π-conjugated molecules with five-membered heteroaromatic rings is intramolecular C–H/C–X coupling reactions of heteroatom-bridged diaryl compounds.

Shimizu, Hiyama, and co-worker reported the palladium-catalyzed synthesis of silafluorenes and related compounds by an intramolecular C–H/C–OTf coupling reaction (Scheme [50]).[79] Interestingly, the obtained silicon-bridged 2-phenylindole exhibited blue photoluminescence in the solid state with extremely high quantum yields.

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Scheme 50 Palladium-catalyzed synthesis of silafluorenes and related compounds by an intramolecular C–H/C–OTf coupling reaction

Shintani, Hayashi, and co-workers applied the reaction in Scheme [50] to the asymmetric synthesis of chiral silafluorene derivatives using a palladium catalyst with a ferrocene-based chiral phosphine ligand (Scheme [51]);[80] the silafluorene derivatives were obtained in high yields and with high enantioselectivity.

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Scheme 51 Asymmetric synthesis of chiral silafluorene derivatives using a palladium catalyst

Glorius and co-workers reported the heterogeneous palladium-catalyzed C–H thiolation of heteroarenes. The products underwent subsequent intramolecular C–H/C–halogen coupling to give [1]benzothieno[3,2-b][1]benzothiophene (BTBT) (Scheme [52]).[81]

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Scheme 52 Synthesis of [1]benzothieno[3,2-b][1]benzothiophene by palladium-catalyzed C–H thiolation of benzothiophene and successive C–H/C–halogen coupling

Intramolecular C–H/C–H coupling reactions can be considered as a more efficient method for the synthesis of condensed polycyclic π-conjugated molecules with five-membered heteroaromatic rings.

You and co-workers successfully synthesized ladder-type π-conjugated molecules with nitrogen and sulfur atoms by rhodium-catalyzed amide directing group assisted intermolecular C–H/C–H coupling, and successive bromination and intramolecular N–H/C–Br coupling reaction (Scheme [53]).[82] Experimental studies and calculations showed that thianaphtheno[3,2-b]indoles have large HOMO–LUMO energy gaps and low-lying HOMO levels, and therefore could potentially be high-performance organic semiconductors.

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Scheme 53 Rhodium-catalyzed amide directing group assisted intermolecular C–H/C–H coupling and successive bromination and intramolecular N–H/C–Br coupling reaction

Paradies and co-worker reported the palladium-catalyzed synthesis of dithieno[3,2-b:2′,3′-d]thiophene (DTT) derivatives by intermolecular dehydrogenative dimerization of benzothiophenes and successive C–S cross coupling (Scheme [54]).[83] The desired products were also obtained in a reverse manner, that is, C–S cross-coupling reaction and successive intramolecular dehydrogenative dimerization. Photophysical (UV and fluorescence spectroscopy) and electrochemical (cyclic voltammetry) data of some products were also reported.

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Scheme 54 Palladium-catalyzed synthesis of dithieno[3,2-b:2′,3′-d]thiophene (DTT) derivatives by intermolecular dehydrogenative dimerization of benzothiophenes and successive C–S cross-coupling reaction

Kuninobu, Kanai, and co-workers successfully synthesized heteroatom-containing ladder-type π-conjugated molecules by a palladium-catalyzed intramolecular oxidative C–H/C–H cross-coupling reaction (Scheme [55]).[84] This reaction provided a wide variety of π-conjugated molecules bearing heteroatoms, such as nitrogen, oxygen, phosphorus, and sulfur, and a phenylene or carbonyl group. A larger π-conjugated molecule was also obtained by double C–H/C–H cross coupling.

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Scheme 55 Palladium-catalyzed intramolecular oxidative C–H/C–H cross-coupling reaction

# 3.6.3

Annulation Reactions

Yoshikai and co-workers reported the one-pot synthesis of benzophosphole oxides, sulfides, and selenides by sequential coupling of an arylzinc reagent, an alkyne, dichloro(phenyl)phosphine, and an oxidant (for example H2O2, S, or Se) (Scheme [56]).[85] A wide variety of π-conjugated molecules containing a benzophosphole moiety were synthesized using this methodology.

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Scheme 56 One-pot synthesis of benzophosphole oxides, sulfides, and selenides by sequential coupling of an arylzinc reagent, an alkyne, dichloro(phenyl)phosphine, and an oxidant

There are two examples of the synthesis of condensed polycyclic π-conjugated molecules with five-membered heteroaromatic rings based on the cleavage of heteroatom–H and C–H bonds. A method for the synthesis of benzophosphole oxides without using organometallic reagents has been reported. Satoh, Miura, and co-workers, and Duan and co-worker independently achieved the synthesis of benzophosphole oxides by silver-mediated dehydrogenative annulation of arylphosphine oxides and alkynes via C–H and P–H bond cleavage (Scheme [57]).[86] [87] The reaction proceeded via the formation of a phosphorus-centered radical. Most of the products showed solid-state fluorescence.

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Scheme 57 Silver-mediated dehydrogenative annulation of arylphosphine oxides and alkynes via C–H and P–H bond cleavage

Jin and co-workers reported the rhodium-catalyzed synthesis of benzoindole derivatives from naphthylcarbamates and internal alkynes (Scheme [58]).[88] In this reaction, copper(II) acetate worked as an oxidant to promote an oxidative [3 + 2] annulation reaction. Interestingly, using stoichiometric silver carbonate instead of silver(I) hexafluoroantimonate/copper(I) acetate/water altered the reaction site dramatically, and benzoquinoline derivatives were obtained.

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Scheme 58 Rhodium-catalyzed synthesis of benzoindole and benzoquinone derivatives from naphthylcarbamates and internal alkynes

There are three examples of the synthesis of condensed polycyclic π-conjugated molecules with five-membered heteroaromatic rings via dual C–H bond activation.

Jiao and co-workers reported the palladium-catalyzed oxidative cycloaromatization of biaryls with internal alkynes using molecular oxygen as an oxidant (Scheme [59]);[89] the reaction proceeded via dual C–H bond activation. Some of the products showed fluorescence.

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Scheme 59 Palladium-catalyzed oxidative cycloaromatization of bi­aryls with internal alkynes

Satoh, Miura, and co-workers reported the rhodium-catalyzed synthesis of naphthothiophene derivatives from 3-phenylthiophenes and internal alkynes via double C–H bond cleavage (Scheme [60]).[90] This oxidative annulation was promoted by a copper salt oxidant.

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Scheme 60 Rhodium-catalyzed synthesis of naphthothiophene derivatives from 3-phenylthiophenes and internal alkynes via double C–H bond cleavage

Li and co-workers reported the rhodium-catalyzed oxidative synthesis of 5,6-disubstituted naphtho[1′,2′:4,5]imidazo[1,2-a]pyridines by annulation of 2-phenylimidazo[1,2-a]pyridines with internal alkynes (Scheme [61]).[91] This reaction proceeded by initial nitrogen-chelation-assisted­ C–H activation at the benzene ring followed by rollover C–H activation.

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Scheme 61 Rhodium-catalyzed oxidative synthesis of a 5,6-disubstituted naphtho[1′,2′:4,5]imidazo[1,2-a]pyridine by annulation of 2-phen­ylimidazo[1,2-a]pyridine with an internal alkyne

# 3.6.4

Miscellaneous

The construction of condensed polycyclic π-conjugated molecular skeletons with five-membered heteroaromatic rings are described in sections 3.6.1 through 3.6.3. In this section, the functionalization of such π-conjugated skeletons is discussed. Marder, Blakey, and co-workers reported the palladium-catalyzed double arylation of benzobisthiazoles (Scheme [62]).[92]

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Scheme 62 Palladium-catalyzed double arylation of benzobisthiazoles

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# 3.7

π-Conjugated Molecules with Nitrogen-Containing­ Six-Membered Heteroaromatics

Highly substituted polyheteroaromatic compounds are useful π-conjugated functional materials that have been used as organic semiconductors or luminescent materials.[93] Acridine derivatives have significant pigment and dye properties, and optical, photochemical, physical, and electrochemical properties.[94] Such compounds have been used as fluorescent probes, as an active medium for dye lasers, and as light-emitting materials in organic light-emitting diodes.

Satoh, Miura, and co-workers reported the copper-mediated­ oxidative synthesis of acridines from triarylmeth­ylamines (Scheme [63]);[95] this reaction proceeded by C–H and C–N bond cleavage. Some products exhibited fluorescence in the solid state.

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Scheme 63 Copper-mediated oxidative synthesis of acridines from triarylmethylamines

A synthesis of highly substituted polyheteroaromatic compounds has also been reported. Chuang, Cheng, and co-workers achieved a rhodium-catalyzed oxidative synthesis of benzo[de]isoquinolino[2,1-a][1,8]naphthyridines and 1H-benzo[de][1,8]naphthyridines from (Z)-N-hydroxybenz­amidines and alkynes (Scheme [64]).[96] The products were formed by multiple C–H bond cleavage and C–C and C–N bond formation; the fluorescent properties of these compounds were also investigated.

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Scheme 64 Rhodium-catalyzed oxidative synthesis of benzo[de]isoquinolino[2,1-a][1,8]naphthyridines

Glorius and co-workers reported the cobalt-catalyzed C–H insertion reaction between heteroarenes and diazo compounds (Scheme [65]).[97] The obtained extended π-conjugated molecules exhibited various colors of fluorescence in both dichloromethane and the solid state.

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Scheme 65 Cobalt-catalyzed C–H insertion reaction between heteroarenes and diazo compounds

# 3.8

Porphyrins

Porphyrins and their metal complexes have unique electronic and optical properties, and they have found use in materials science as functional dyes, artificial photosynthesis, dye-sensitized solar cells, photodynamic therapy, conductive organic materials, light-emitting materials, near-infrared­ dyes, non-linear optical materials, molecular wires, metal ligands, and supramolecules.[98]

Shinokubo, Osuka, and co-workers reported the iridium-catalyzed C–H borylation of porphyrins in the β-position (Scheme [66]).[99] This is a rare example of the β-selective functionalization of the porphyrin ring. The β-borylated porphyrins are useful building blocks as demonstrated by examples of palladium-catalyzed oxidative dimerization[99a] and the Suzuki–Miyaura cross-coupling reaction.[99b]

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Scheme 66 Iridium-catalyzed C–H borylation of porphyrins in the β-position

Yorimitsu, Osuka, and co-workers reported the palladium-catalyzed C–H arylation of porphyrins (Scheme [67]).[100] The arylation reaction proceeded in the β-position of the porphyrin ring. The regioselectivity is controlled by steric factors. UV-vis absorption spectra showed the existence of a small conjugation between the porphyrin core and the β-aryl groups.

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Scheme 67 Palladium-catalyzed C–H arylation of porphyrins

Kuninobu, Takai, and co-worker reported the rhenium-catalyzed synthesis of naphthalene-substituted aryl bromides or iodides via C–H bond activation, and their introduction into a tetraethynylporphyrin using the palladium-catalyzed Sonogashira coupling reaction (Scheme [68]).[101] A series of novel meso-substituted tetraalkynylporphyrins that contain naphthalene moieties were obtained using this method.

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Scheme 68 Synthesis of meso-substituted tetraalkynylporphyrins

# 3.9

Miscellaneous (π-Conjugated Molecules)

In 2009, Miura and co-workers developed a method for the copper-mediated direct arylation of 1,3,4-oxadiazoles and 1,2,4-triazoles (Scheme [69]).[102] They also applied this reaction to the synthesis of carbazole-ligated arylated 1,3,4-oxadiazoles that are expected to be applied as organic light-emitting diodes.

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Scheme 69 Copper-mediated C–H arylation of 1,3,4-oxadiazoles

Dithienylethenes are organic photochromic compounds, and aryl groups substituted on dithienylethenes can control the absorption properties and thus the color change of the photochromic reaction. Itami, Shinokubo, and co-workers and Guerchais, Doucet, and co-workers have reported the palladium-catalyzed C–H arylation of thienyl groups (Scheme [70]).[103] [104] Unsymmetrical substituted dithienyl­ethenes were also synthesized.

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Scheme 70 Palladium-catalyzed C–H arylation of thienyl groups

3,6-Di-2-thienyl-1,4-dioxo-2,5-dihydropyrrolo[3,4-c]pyrroles (DTDPPs) and their related dioxopyrrolopyrrole derivatives are used in the construction of charge-transport materials for p-channel, n-channel, and ambipolar organic field-effect transistors (OFETs) and light-absorbing hole-transport materials for organic photovoltaics (OPVs). DTDPP­ derivatives are typically synthesized by traditional transition-metal-catalyzed cross-coupling reactions, either between a (hetero)aryl halide and an organometallic DTDPP­ derivative, or between a halide derivative of a DTDPP­ and an organometallic hetero(arene) reagent. Marder and co-workers reported a palladium-catalyzed direct C–H arylation of dithienyldioxopyrrolopyrroles (Scheme [71]).[105] [106] The oxidation and reduction potentials can both be tuned over a range of about 0.4 V, while the absorption and fluorescence maxima are relatively constant (each varying by ca. 0.1 eV).

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Scheme 71 Palladium-catalyzed C–H arylation of dithienyldioxopyrro­lopyrroles

In 2012, Dehaen and co-workers reported the palladium-catalyzed C–H arylation of boron-dipyrromethenes (BODIPYs) at the 3- and 3,5-positions (Scheme [72]);[107] other palladium-catalyzed arylation methods have been reported.[108] Although the selectivity must be improved, monoarylated BODIPYs could be used for the synthesis of extended π-conjugated unsymmetrical 3,5-arylated BODIPYs. Large Stokes shifts were observed in the case of arylated BODIPYs.

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Scheme 72 Palladium-catalyzed C–H arylation of BODIPYs at the 3- and 3,5-positions

Yorimitsu, Oshima, and co-workers reported the palladium-catalyzed C–H arylation of tetrathiafulvalenes with bromoarenes (Scheme [73]).[109] Cyclic voltammetry of the CT complexes of the synthesized tetraarylthiafulvalenes and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or tetracyano-1,4-benzoquinone (TCQN) were examined.

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Scheme 73 Palladium-catalyzed C–H arylation of tetrathiafulvalenes with bromoarenes

1,2-Dihydro-1,2-azaborine is a BN isostere of monocyclic aromatic compounds. The unique aromaticity of 1,2-aza­borine has attracted much attention in medicinal chemistry and materials science. Liu and co-workers reported the regioselective iridium-catalyzed C–H borylation of B-substituted 1,2-azaborines (Scheme [74]).[110] The 1,2-azaborine–boron complex was derivatized by several transformations and the products exhibited higher photoluminescence than that of a carbonaceous isostere.

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Scheme 74 Regioselective iridium-catalyzed C–H borylation of a B-substituted 1,2-azaborine

Bowl-shaped polycyclic aromatic compounds have received much attention due to their unique physical properties and partial fullerene- and carbon-nanotube-like structures. The introduction of heteroatoms into bowl-shaped polyaromatic compounds is expected to create compounds with new, useful properties for further application. However, there are scant methods reported for the synthesis of heteroatom-doped derivatives. Ito, Nozaki, and co-worker reported the synthesis of pentabenzoazacorannulene via 1,3-dipolar cyclization of an azomethine ylide and intramolecular palladium-catalyzed C–H cyclization (Scheme [75]).[111] The synthesized pentabenzoazacorannulene exhibited longer emission wavenumbers of fluorescence than those of corannulene.

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Scheme 75 Synthesis of pentabenzoazacorannulene via 1,3-dipolar cyclization of azomethine ylide and intramolecular palladium-catalyzed C–H cyclization

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# 4

Miscellaneous (Excluding Polymers and π-Conjugated Molecules)

Metal–organic frameworks (MOFs) are highly porous crystalline hybrid materials that are expected to be applied to various areas, such as gas storage and separation, catalysis, and drug delivery. Glorius and co-workers developed a method for the direct C–H arylation of indole-derived UMCM-1 (University of Michigan Crystalline Material-1)-type MOF in the presence of a palladium catalyst (Scheme [76]).[112] [113] The phenylated UMCM-1-Ph-indole showed better nitrogen absorption and desorption abilities than the original UMCM-1-indole.

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Scheme 76 Palladium-catalyzed direct C–H arylation of an indole-derived UMCM-1-type MOF

Perfluorinated arene-thiophenes play an important role as useful materials for organic devices, such as organic light-emitting diodes (OLEDs) and field-effect transistors (FETs). Zhang and co-workers reported the C–H coupling reaction between terthiophene and electron-deficient perfluoroarenes that gave products which could be used as an n-type organic semiconductor (Scheme [77]).[114]

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Scheme 77 C–H Coupling reaction between terthiophene and electron-deficient perfluoroarenes

C–H Functionalization an also be applied to metal complexes. In 2012, Doucet, Guerhais, and co-workers reported the first C–H arylation of a tris-cyclometalated iridium(III) complex bearing 2,2′-thienylpyridine ligands (Scheme [78]).[115] This method enabled the synthesis of new iridium complexes in only one step, and the photophysical properties of the complexes could be tuned by functionalization of the ligands.

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Scheme 78 Palladium-catalyzed C–H arylation of tris-cyclometalated iridium(III) complex bearing 2,2′-thienylpyridine ligands

Mori and co-workers reported the synthesis of 2,5-diarylthiazoles via tandem C–H coupling with aryl halides (Scheme [79]).[116] The hetero-substituted 2,5-diarylthiazoles showed not only blue fluorescence in chloroform, but also liquid crystal characteristics that showed characteristic texture for a nematic phase.

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Scheme 79 Synthesis of 2,5-diarylthiazoles via tandem C–H coupling with aryl halides

Dendrimers are highly ordered and branched macromolecules that are used in both bioscience and materials science. Smith and co-workers synthesized a polyphenylene dendron using the repetitive C–H borylation of arenes and the Suzuki–Miyaura cross-coupling reaction as key reactions (Scheme [80]).[117] [118]

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Scheme 80 Synthesis of a polyphenylene dendron using the repetitive C–H borylation of arenes and the Suzuki–Miyaura cross-coupling reaction

# 5

Outlook and Conclusions

In conclusion, many types of practical C–H bond transformation have been reported for the synthesis of functional materials and their candidates. The development of synthetic organic reactions directed toward organic functional materials began about 10 years ago, and the examples of such transformations have increased dramatically in the past few years. As a result of the ceaseless efforts of many organic chemists, different types of organic functional molecules can be synthesized using these transformations in a practical manner. However, most of the products can also be synthesized by other methods. Of course, it is very important to improve the efficiency and utility of synthetic organic reactions and further developments are expected; however, it is also desirable that the synthesis of organic functional molecules that cannot be synthesized, or are difficult to synthesize, using previous methods, is achieved by the development of C–H bond transformations. In addition, the creation of new compounds with new structures, properties, and/or concepts is also highly desirable.

Abbreviations

Bpin = 4,4,5,5-tetramethyl-1,3,2-dioxaboryl

CPDO = 5H-cyclopenta[1,2-b:5,4-b′]dipyridin-5-one

DavePhos = 2-(dicyclohexylphosphino)-2′-(dimethylamino)biphenyl

DMAc = N,N-dimethylacetamide

DCE = 1,2-dichloroethane

4,4′-dmbpy = 4,4′-dimethyl-2,2′-dipyridyl

dtbpy = 4,4′-di-tert-butyl-2,2′-dipyridyl

PEPPSI-IPr = [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride

SPhos = 2-(dicyclohexylphosphino)-2′,6′-dimethoxybiphenyl

TBAB = tetrabutylammonium bromide

Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene


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Acknowledgment

We are grateful for financial support by CREST from JST and Grant-in-Aid for Scientific Research (B) from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.



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Scheme 1 Ruthenium-catalyzed regioselective step-growth copolymerization of acetophenones and α,ω-dienes
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Scheme 2 Rhenium-catalyzed synthesis of polyimide derivatives via insertion of diisocyanates into the C–H bond of aromatic dicarboximidates
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Scheme 3 Palladium-catalyzed synthesis of oligothiophenes by C–H arylation with 2-bromo-3-hexylthiophene followed by halogen exchange
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Scheme 4 Rhodium-catalyzed synthesis of poly(pyrazolylnaphthalene)s
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Scheme 5 Palladium-catalyzed polymerization of 3-alkyl-2-iodothiophenes using a cross-coupling reaction
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Scheme 6 Polymerization of 2-bromo-3-hexylthiophenes using the Herrmann’s catalyst/tris[2-(dimethylamino)phenyl]phosphine system
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Scheme 7 Palladium/phosphine-catalyzed copolymerization between dibromocarbazoles and tetrafluorobenzene
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Scheme 8 Rhodium-catalyzed C–H borylation of polyethylethylenes
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Scheme 9 Iridium-catalyzed C–H borylation of polystyrenes
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Scheme 10 Polymerization of 2-vinylpyridines using an yttrium ene–diamido complex
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Scheme 11 Aminofluorenes by a rhodium-catalyzed intramolecular C–H/C–H coupling reaction
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Scheme 12 Iridium-catalyzed synthesis of fluorenols via C–H activation
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Scheme 13 Rhodium-catalyzed synthesis of multisubstituted silylindenes using hydrosilanes and diarylacetylenes
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Scheme 14 Rhodium-catalyzed synthesis of indenols and fulvenes via C–H bond activation
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Scheme 15 Rhodium-catalyzed synthesis of anthrylazoles from 2-phenylazoles and internal alkynes
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Scheme 16 Palladium-catalyzed synthesis of highly substituted naphthalene derivatives from arenes and internal alkynes
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Scheme 17 Rhodium-catalyzed synthesis of highly substituted arenes by formal oxidative [2+2+2]-cycloaddition reactions
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Scheme 18 Iridium-catalyzed synthesis of phenanthrene derivatives from 2-arylbenzoyl chlorides and internal alkynes
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Scheme 19 Palladium-catalyzed oxidative synthesis of dibenzo[a,e]pentalenes by annulative dimerization of diarylacetylenes
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Scheme 20 Palladium-catalyzed cascade crossover annulation between o-alkynylaryl halides and diarylacetylenes
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Scheme 21 Rhenium-catalyzed synthesis of isobenzofurans from aromatic imines and aldehydes via C–H bond activation
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Scheme 22 Cobalt-catalyzed synthesis of aromatic aldimines with a branched alkyl chain by ortho-selective insertion of styrenes
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Scheme 23 Palladium-catalyzed synthesis of [6]phenacenes by two Suzuki–Miyaura cross-coupling reactions and successive intramolecular C–H/C–Cl coupling reactions
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Scheme 24 Palladium-catalyzed C–H arylation of arenes using aryltin reagents
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Scheme 25 Ruthenium-catalyzed synthesis of multi-arylated acenes by ruthenium-catalyzed C–H arylation and successive transformations
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Scheme 26 Palladium-catalyzed synthesis of substituted triphenylenes between 2-iodobiphenyls and a 2-bromobenzyl alcohol
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Scheme 27 Palladium-catalyzed synthesis of triphenylenes using teraryl sulfonium salts
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Scheme 28 Palladium-catalyzed C–H arylation of triphenylene
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Scheme 29 Ruthenium-catalyzed C–H arylation reaction to provide tetraarylated perylene diimides
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Scheme 30 Palladium-catalyzed C–H alkylation of perylene diimides
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Scheme 31 Synthesis of water-soluble perylene diimides by palladium-catalyzed C–H phosphonethylation
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Scheme 32 Iridium-catalyzed C–H borylation of perylene diimides
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Scheme 33 Ruthenium-catalyzed C–H borylation, bromination, and Stille coupling of perylene diimides
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Scheme 34 Iridium-catalyzed C–H borylation of naphthalenediimides
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Scheme 35 Iridium-catalyzed selective C–H borylation of polycyclic aromatic hydrocarbons
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Scheme 36 Iridium-catalyzed C–H polyborylation of corannulene
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Scheme 37 Iridium-catalyzed C–H borylation of hexabenzocoronene
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Scheme 38 Palladium-catalyzed C–H arylation of pyrenes
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Scheme 39 Synthesis of decakis(4-chlorophenyl)corannulene via C–H arylation
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Scheme 40 Synthesis of warped nanographene via C–H borylation of corannulene
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Scheme 41 Palladium-catalyzed K-region-selective annulative π-extension for the synthesis of graphenes and nanographenes via C–H bond transformations
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Scheme 42 Rhodium-catalyzed synthesis of silafluorene derivatives from biphenyl(hydro)silanes
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Scheme 43 Asymmetric synthesis of spirosilabifluorenes
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Scheme 44 Palladium-catalyzed synthesis of phosphafluorene (dibenzophosphole) oxides
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Scheme 45 Palladium-catalyzed regioselective C–H borylation of 2-phenylpyridines
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Scheme 46 Iridium-catalyzed direct and ortho-selective C–H silylation of 2-phenylpyridines
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Scheme 47 Palladium-catalyzed C–H fluorosilylation of 2-phenylpyridines
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Scheme 48 Palladium-catalyzed synthesis of dibenzofuran derivatives from 2-arylphenols by an intramolecular oxidative C–H/O–H coupling reaction
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Scheme 49 Palladium-catalyzed synthesis of benzothieno[2,3-b]indoles via dehydrative–dehydrogenative double C–H sulfuration
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Scheme 50 Palladium-catalyzed synthesis of silafluorenes and related compounds by an intramolecular C–H/C–OTf coupling reaction
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Scheme 51 Asymmetric synthesis of chiral silafluorene derivatives using a palladium catalyst
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Scheme 52 Synthesis of [1]benzothieno[3,2-b][1]benzothiophene by palladium-catalyzed C–H thiolation of benzothiophene and successive C–H/C–halogen coupling
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Scheme 53 Rhodium-catalyzed amide directing group assisted intermolecular C–H/C–H coupling and successive bromination and intramolecular N–H/C–Br coupling reaction
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Scheme 54 Palladium-catalyzed synthesis of dithieno[3,2-b:2′,3′-d]thiophene (DTT) derivatives by intermolecular dehydrogenative dimerization of benzothiophenes and successive C–S cross-coupling reaction
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Scheme 55 Palladium-catalyzed intramolecular oxidative C–H/C–H cross-coupling reaction
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Scheme 56 One-pot synthesis of benzophosphole oxides, sulfides, and selenides by sequential coupling of an arylzinc reagent, an alkyne, dichloro(phenyl)phosphine, and an oxidant
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Scheme 57 Silver-mediated dehydrogenative annulation of arylphosphine oxides and alkynes via C–H and P–H bond cleavage
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Scheme 58 Rhodium-catalyzed synthesis of benzoindole and benzoquinone derivatives from naphthylcarbamates and internal alkynes
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Scheme 59 Palladium-catalyzed oxidative cycloaromatization of bi­aryls with internal alkynes
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Scheme 60 Rhodium-catalyzed synthesis of naphthothiophene derivatives from 3-phenylthiophenes and internal alkynes via double C–H bond cleavage
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Scheme 61 Rhodium-catalyzed oxidative synthesis of a 5,6-disubstituted naphtho[1′,2′:4,5]imidazo[1,2-a]pyridine by annulation of 2-phen­ylimidazo[1,2-a]pyridine with an internal alkyne
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Scheme 62 Palladium-catalyzed double arylation of benzobisthiazoles
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Scheme 63 Copper-mediated oxidative synthesis of acridines from triarylmethylamines
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Scheme 64 Rhodium-catalyzed oxidative synthesis of benzo[de]isoquinolino[2,1-a][1,8]naphthyridines
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Scheme 65 Cobalt-catalyzed C–H insertion reaction between heteroarenes and diazo compounds
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Scheme 66 Iridium-catalyzed C–H borylation of porphyrins in the β-position
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Scheme 67 Palladium-catalyzed C–H arylation of porphyrins
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Scheme 68 Synthesis of meso-substituted tetraalkynylporphyrins
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Scheme 69 Copper-mediated C–H arylation of 1,3,4-oxadiazoles
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Scheme 70 Palladium-catalyzed C–H arylation of thienyl groups
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Scheme 71 Palladium-catalyzed C–H arylation of dithienyldioxopyrro­lopyrroles
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Scheme 72 Palladium-catalyzed C–H arylation of BODIPYs at the 3- and 3,5-positions
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Scheme 73 Palladium-catalyzed C–H arylation of tetrathiafulvalenes with bromoarenes
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Scheme 74 Regioselective iridium-catalyzed C–H borylation of a B-substituted 1,2-azaborine
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Scheme 75 Synthesis of pentabenzoazacorannulene via 1,3-dipolar cyclization of azomethine ylide and intramolecular palladium-catalyzed C–H cyclization
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Scheme 76 Palladium-catalyzed direct C–H arylation of an indole-derived UMCM-1-type MOF
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Scheme 77 C–H Coupling reaction between terthiophene and electron-deficient perfluoroarenes
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Scheme 78 Palladium-catalyzed C–H arylation of tris-cyclometalated iridium(III) complex bearing 2,2′-thienylpyridine ligands
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Scheme 79 Synthesis of 2,5-diarylthiazoles via tandem C–H coupling with aryl halides
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Scheme 80 Synthesis of a polyphenylene dendron using the repetitive C–H borylation of arenes and the Suzuki–Miyaura cross-coupling reaction