Download PDF
Synlett 2023; 34(18): 2085-2096
DOI: 10.1055/a-2036-1151
account
Modern Boron Chemistry: 60 Years of the Matteson Reaction

Recent Advances in the Preparation and Asymmetric Transformation of α-Haloboron Compounds

Dong Wang
,
Tao XU  ∗

This work was supported by the National Natural Science Foundation of China (Grant No. 22071183), the Science and Technology Commission of Shanghai Municipality (19DZ2271500), and the Open Research Fund of Key Laboratory of the Ministry of Education for Advanced Catalysis Materials and Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces.
› Further Information
 
 PDF Download Permissions and Reprints All articles of this category


Abstract

α-Haloboron compounds are very versatile synthons in organic synthesis. They can be transformed into several kinds of skeletons via Matteson homologation reaction, cross-coupling or other strategies based on the carbon–halo or carbon–boron bond. In recent years, many important advances have been achieved in the upstream and downstream chemistry of these compounds. This review comprehensively summarizes their current synthetic methods and asymmetric couplings with nickel catalysts.

1 Introduction

2 The Preparation of α-Haloboron Compounds

3 The Asymmetric Transformation of α-Haloboron Compounds

4 Conclusion


#

Key words

boron chemistry - α-haloboron compounds - asymmetric coupling - nickel catalysis - homologation reaction

Biographical Sketches

Zoom Image

Dong Wang was born in ­Dezhou city of Shandong Province in 1993. He received his B. S. at Dezhou University in 2016. Then, he continued his studies at School of Petrochemical Engineering at Changzhou University and received a master’s degree with Professor Xiaofeng Tong in 2019. He entered the School of Chemical Science and Engineering at Tongji University for his Ph.D. in 2020, and joined the laboratory of Professor Tao XU. His research focuses on deoxygenative difunctionalization of carbonyls.

Zoom Image

Tao XU received his B. S. at East China University of Science and Technology in 2007. Then, he continued his studies at ­Shanghai Institute of Organic Chemistry, CAS (SIOC), joined the laboratory of Professor ­Guosheng Liu, and gained a Ph.D. in 2012. After that, he worked in WuXi AppTec Company, Ltd for one year. In 2013, he started his postdoctoral research working with Professor Xile Hu at École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. Tao began his independent career at Tongji University in 2017. Recently, his research focus has been on developing new methodologies for asymmetric carbon–carbon bond formation and multi-catalyst relay systems.

1

Introduction

α-Haloboron compounds are multifunctional and versatile synthons in organic synthesis based on the inherent carbon–halo bond and boron group, both of which can be converted into many other functional groups under transition metal-free or transition-metal-catalyzed conditions. Meanwhile, as a unique geminal difunctional skeleton that has one electrophile and one nucleophile, complex molecules can be obtained within several simple steps through the use of this type of compound as an intermediate. More importantly, with the recent development of asymmetric chemistry, several chiral compounds including those with enantioenriched quaternary carbon centers could be easily accessed from these α-haloboron substrates. Therefore, increasing efforts have been made to develop the upstream and downstream chemistry of α-haloboron compounds.

However, compared with numerous studies on the racemic transformation of these substrates or the stereospecific conversion of chiral α-haloborons, far fewer reports were published on their preparation and asymmetric transformation before and at the beginning of this century. Since then, several elegant works have been reported in this field during the last decade. This review aims to comprehensively highlight recent advances in emerging synthesis methods for this type of compound. The asymmetric transformation of racemic α-haloboronates with nickel catalysts developed in our group and others have been also included.


# 2

The Preparation of α-Haloboron Compounds

When it comes to the synthetic routes to α-haloboron compounds, an important and famous milestone was the Matteson homologation reaction, which was first reported in 1963.[1] After the highly stereoselective one-carbon elongation of alkyl boronic esters was developed, the application of the strategy to the synthesis of α-haloboron compounds was also investigated by the same group (Scheme [1]).[2] Although there were several known routes to these compounds before that, they typically lacked the generality and convenience needed for widespread synthetic utility.[3] It was found that the homologation of boronic esters with (dichloromethyl)lithium (DCMLi) could provide a straightforward route. A series of substrates including primary, secondary, or tertiary alkyl, cycloalkyl, alkenyl, allyl, and aryl boronic esters can be applied with this method to form the corresponding α-chloroboronic esters (2), which renders it a very highly efficient process.[4] Despite the strong base (butyllithium) and harsh conditions involved in the preparation of (dichloromethyl)lithium, this method still has good functional group compatibility. Some functional substituents in the boronic esters, such as α-benzyloxy, β- or remote ester, or a remote ketal were tolerated with this protocol. Because of this, it has become one of the main methods used since it was reported. The α-bromo or α-iodoboronate can be obtained via halo-exchange with the corresponding halide salts.[5] A continuous-flow procedure for the synthesis of DCMLi and application in this homologation of aryl boronic esters were disclosed by Hafner and Sedelmeier and co-workers in 2017.[6]

Zoom Image
Scheme 1 Matteson homologation reaction to α-chloroboron compounds

Then, in 1993, the Srebnik group reported another preparation method from 1,1-bimetalloalkanes (Scheme [2]).[7] Hydrozirconation of vinyl-9-BBN derivatives (3) with Schwartz’s reagent, H(Cl)ZrCp2, could provide 1,1-demetalloalkanes of boron and zirconium (4). By selective cleavage of the C–Zr bond with bromide, a method to access α-bromoboron compounds was achieved. However, only several examples with simple functional groups (alkyl, phenyl, alkyl chloride) were given.

Zoom Image
Scheme 2 The preparation of α-bromoboron compounds with Schwartz’s reagent

In 1994, hydroboration of 1-halo-1-alkenes (6) with catecholborane (7) with a rhodium catalyst for the α-haloboron substrates (8) was disclosed by Elgendy and co-workers (Scheme [3]).[8]

Zoom Image
Scheme 3 Hydroboration of 1-halo-1-alkenes with catecholborane

Meanwhile, due to the limited availability of 1-haloalkenes, the authors developed a more useful method by reaction of pinanediol dichloromethylboronate (10) with organometallic reagents,[9] which has since been commonly used (Scheme [4]).[5a] [10]

Zoom Image
Scheme 4 The preparation of α-chloroboron compounds with dichloromethylboronate

After that, for a long time, there were very few works focused on the development of synthetic methods for this type of compound. However, in 2012, Časar and co-workers reported an iridium-catalyzed chemoselective and enantioselective hydrogenation of (1-chloro-1-alkenyl)boronic esters (12) to afford chiral α-chloroboronates (13) (Scheme [5]A).[11] Excellent conversion, high chemoselectivities (with dechlorinated byproducts in the range of 3–19%), and enantioselectivities of up to 94% enantiomeric excess (ee) were achieved. In addition, the reaction with (1-bromo)-1-alkenylboronic esters (14) was also studied (Scheme [5]B).[12] However, the special starting materials and the high hydrogen pressure bring some limitations for application of the method.

Zoom Image
Scheme 5 The preparation of chiral α-haloboron compounds via hydrogenation of (1-chloro-1-alkenyl)boronic esters

Alkenyl N-methyliminodiacetyl (MIDA) boronates (16) are easily accessible through several synthetic routes; therefore, they are also employed to afford α-haloboron compounds. In 2016, the Wang group developed a one-pot oxidative difunctionalization of alkenyl MIDA boronates for the formation of α-halo-β-carbonyl boronates (Scheme [6]).[13] By using different oxidants, C–F, C–Cl, C–Br, or C–I bonds can be introduced. Nevertheless, the aryl substitution in the alkenyl MIDA boronates was necessary.

Zoom Image
Scheme 6 The preparation of α-halo-β-carbonyl boronates via oxidative difunctionalization of alkenyl MIDA boronates

In 2020, Grygorenko and co-workers further expanded the product scope from aryl ketones to aliphatic ketones (20) through regioselective bromohydroxylation (19) followed by oxidation of the alcohol group with Dess–Martin periodinane (Scheme [7]).[14]

Zoom Image
Scheme 7 The preparation of α-bromo-β-carbonyl boron compounds via bromohydroxylation

At around the same time, the Wang group also studied this halohydroxylation, including chloro-, bromo- and iodohydroxylation with the alkenyl MIDA boronates as the starting material (Scheme [8]A).[15] Interestingly, a syn-addition process was detected using Cl+ or Br+ as the halogen source (22-a, 22-b), while trans-addition products were obtained when I+ was employed (22-c). A proposed mechanism was given by the authors to explain these results. Moreover, an iodofluorination of alkenyl MIDA boronates was also developed by the same group (Scheme [8]B).[16]

Zoom Image
Scheme 8 Halohydroxylation and iodofluorination of alkenyl MIDA boronates

Wang and co-workers subsequently reported a pattern to deliver α-haloboron compounds (27) via a photochemical radical C–H halogenation of benzyl MIDA boronates (26). With this protocol, fluorination, chlorination, and bromination were achieved (Scheme [9]). Mechanistic studies showcased an activating effect of the B(MIDA) group on the reaction. In addition, halogenation of α-hydroxyl MIDA boronates provides an alternative route for these α-halo MIDA boronates, which was reported by the Sharma group.[17]

Zoom Image
Scheme 9 The preparation of α-haloboron compounds via photochemical radical C–H halogenation of benzyl MIDA boronates

Compared with alkylboron compound R-BMIDA, the C–B bond transformation of alkylboron substrates represented by pinacol alkylboronates (RBPin) and potassium alkyltrifluoroborate (RBF3K) is more common and convenient. Therefore, efforts were also taken on the synthesis of α-haloboronates wherein BPin or BF3K was attached. In 2020, Ueda and co-workers found that the addition reaction between perfluoroalkyl iodides and potassium vinyl-BK3F (30) could provide a method for the synthesis of α-iodoboronates in the presence of 20 mol% Et3B as the radical initiator via an atom-transfer radical addition (ATRA) process (Scheme [10]A).[18] Some other active iodides, such as iodoacetate and iodoacetonitrile, can be also utilized. After that, in 2021, the Song group disclosed another method under photoinduced weak-base-catalyzed conditions (Scheme [10]B).[19] The reaction can give the target products in moderate to good yields. When bromotrichloromethane was used, the corresponding desired product α-bromoboronate (33-b) was also delivered in high yield. A radical process was proposed by the authors. However, unactivated alkyl halides were not applicable to these systems.

Zoom Image
Scheme 10 The preparation of α-haloboron compounds via atom-transfer radical addition

In 2021, the Morken group published a nickel-catalyzed carbozincation of vinylboronic esters (34) to afford enantiomerically enriched α-borylzinc reagents (35), which can further undergo bromination and chlorination (Br2 and trichloroisocyanuric acid/CeCl3, respectively) to furnish the chiral α-haloboronates (37, 38) (Scheme [11]).[20] Nevertheless, the absolute configurations of the halogenation products are opposite to the compounds obtained from reactions with allylic electrophiles.

Zoom Image
Scheme 11 The preparation of chiral α-haloboron compounds via nickel-catalyzed carbozincation of vinylboronic esters

In the same year, an enantioselective catalytic 1,2-boronate rearrangement for the synthesis of α-chloro pinacol boronic esters from boronic esters was reported by the ­Jacobsen group with a lithium-isothiourea-boronate complex (Li-L4) as the real catalyst (Scheme [12]).[21] It was proposed that the complex can promote the rearrangement through a dual-lithium-induced chloride abstraction orchestrated by Lewis basic functionality on the catalyst scaffold. The chiral α-chloroboronates can be obtained in good yields and excellent enantioselectivities.

Zoom Image
Scheme 12 The preparation of chiral α-chloroboronates via enantioselective catalytic 1,2-boronate rearrangement

Recently, the Gaunt group reported a visible light-mediated bimetallic synergistic catalytic system to convert diaryl iodonium salts (42), vinyl borates (32), and simple metal chlorides into stable and versatile α-chloroboronic acid ester compounds (43) (Scheme [13]).[22] However, the specificity of their substrates makes the method only suitable for the synthesis of β-aryl substituent products.

Zoom Image
Scheme 13 The preparation of β-aryl-α-chloroboronates

Despite these great advances, developing efficient synthetic routes to access versatile α-haloboronates was still in high demand, especially considering the easily available starting materials and catalysts, the simple operational procedures, environmentally benign conditions, and practical synthetic application (large-scalable). To this end, very recently, we reported a very convenient and modular method to construct α-haloboronates or chiral α-chloroboronates via a deoxygenative difunctionalization of carbonyls (DODC) strategy.[23] We found that for the aldehyde (44-a), after the copper-catalyzed borylation, the in-situ formed intermediate can be easily converted into α-chloroboronate product (46-a) in 90% yield by simple reaction with TMSCl in acetone solvent (Scheme [14]). Other types of halo sources (such as LiCl, tetrabutylammonium chloride (TBAC)) or other common solvents did not give any of the product.

Zoom Image
Scheme 14 The preparation of α-haloboronates via deoxygenative difunctionalization of carbonyls
Zoom Image
Scheme 15 The preparation of secondary α-haloboronates from aldehydes

With these conditions, a diverse set of aldehydes bearing various functional groups, even for those that are sensitive to strong bases or organometallic reagents, can be compatible, thus providing a protocol to synthesize complex skeletons (Scheme [15]). Meanwhile, α-bromo- and α-iodo-boronates can be conveniently accessed just by replacing the nucleophile TMSCl with TMSBr or TMSI. In the previous routes, these products were generally obtained from α-chloroboronates via the halo-exchange process, which unfortunately leads to extra steps and purification issues. In addition, not only the aliphatic aldehydes but also aryl aldehydes are successfully utilized with this method. Moreover, this method is very large-scalable. The gram-scale reactions with various candidates proceeded smoothly under these deoxygenative difunctionalization conditions.

Zoom Image
Scheme 16 The preparation of tertiary α-haloboronates from ketones
Zoom Image
Scheme 17 The preparation of chiral secondary and tertiary α-chloroboronates

Additionally, tertiary α-haloboronates (48) can be also obtained starting from ketone materials. Essentially, these tertiary products cannot be obtained or cannot be easily prepared by the aforementioned methods. In fact, there were only very few methods available to construct tertiary α-haloboronates, and these typically required strong oxidants or special types of compounds.[22] [24] With our method, these products can be generated very easily with aliphatic ketone substrates as the starting materials, although the aryl ketones failed under the current conditions (Scheme [16]). Cyclic or acyclic ketone candidates with many kinds of functional groups can be readily transformed into the corresponding products with similarly high yields.

Zoom Image
Scheme 18 Coupling with alkylzinc reagents to access chiral secondary boronic esters and applications of the method to homologation processes

More importantly, we found that, with the commercially available chiral catalyst, this method could be applied for the synthesis of chiral α-chloroboronates (41) (Scheme [17]). Compared with the works from Časar[11] , [12] and Jacobsen,[21] our method can be utilized for the construction of both chiral secondary and tertiary α-chloroboronates. For the latter, to our knowledge, this was the first catalytic protocol to obtain this type of product (Scheme [17]B).

Zoom Image
Scheme 19 An example of asymmetric reductive coupling of α-bromoboronic ester with aryl iodide
Zoom Image
Scheme 20 The Ni/photoredox-catalyzed asymmetric reductive coupling of α-chloroboronates with aryl halides

# 3

The Asymmetric Transformation of α-Haloboron Compounds

In addition to studies on the preparation of α-haloboron compounds, efforts were also taken on the transformation of these kinds of products. So far, there have been many reports of racemic conversions.[5b] [c] [10c] [25] In contrast, asymmetric transformations, which would offer more important ways to apply these compounds in organic synthesis, remain very limited. As part of the research interests of our group in this field, herein, we briefly summarize the recently developed asymmetric couplings of α-haloboronates with nickel catalysts.

In 2016, the Fu group reported the first example of asymmetric cross-coupling of α-haloboronates (50, 51) with alkylzinc reagents (52) to furnish the versatile chiral secondary alkylboronic esters (53) with nickel catalyst in good yields and excellent enantioselectivities (Scheme [18]A).[5a] The product can be converted into another α-chloroboronate with DCMLi via an iterative homologation process, then further coupled with other alkylzinc reagents by this newly developed method. By virtue of the appropriate enantiomer of the nickel-L* catalyst for each carbon–carbon bond-forming process, any of the four possible diastereomers of the target alkylboronic esters (54, ent-54, 55, ent-55) can be obtained from a single starting material (Scheme [18]B).

In 2018, the Martin group published a nickel-catalyzed racemic reductive cross-coupling of α-bromoboronic esters with aryl halides, wherein an asymmetric example with only 27% ee was given in the presence of a chiral ligand L8 (Scheme [19]).[5b]

To solve this challenge, we envisioned that the dual nickel/photoredox catalytic system could be a suitable tool. Indeed, we found that, in the presence of a nickel catalyst and 4CzIPN as the photoredox catalyst, the asymmetric coupling of α-chloroboronates with aryl halides can proceeded smoothly to give the target products (60) in excellent enantioselectivities and high yields (Scheme [20]A).[26] It is worth mentioning that the traditional reductants used in nickel-catalyzed reductive cross-couplings, such as metal reductants zinc and magnesium, or organic reagents B2Pin2 and tetrakis(dimethylamino)ethylene (TDEA), only give trace amounts or none of the product (Scheme [20]B), further highlighting the great superiority of this dual catalytic regime.

Zoom Image
Scheme 22 The nickel-catalyzed asymmetric coupling of perfluoroalkyl-substituted α-iodoboronates with aryl halides

Very interestingly, under these conditions, α-bromoboronate (56-b) only gave a low yield and only 2% GC yield was detected with the more active α-iodoboronate (51-a) (Scheme [21]A). Mechanistic studies revealed that the photocatalytic cycle can reduce the α-chloroboronate to form an alkyl radical while the radical-trapped product can be obtained in 23% yield with stoichiometric Ni(cod)2 (Scheme [21]B). Therefore, a proposed catalytic cycle was given based on these results (Scheme [21]C).

Zoom Image
Scheme 21 Mechanistic studies on Ni/photoredox-catalyzed asymmetric reductive coupling of α-chloroboronates with aryl halides

The enantioselective construction of perfluoroalkylated molecules has important applications in material science, agrochemistry, and medicinal chemistry. Therefore, in 2021, we developed a nickel-catalyzed asymmetric coupling of perfluoroalkyl-substituted α-iodoboronates with aryl halides (Scheme [22]A).[27] The α-iodoboronates can be easily prepared from commercially available perfluoroalkyl iodides and vinyl boronates according to Song’s method. To achieve this asymmetric coupling, the additive tetrabutylammonium chloride (TBAC) was crucial; without TBAC, no product was formed (Scheme [22]B).

The role of TBAC was further studied in detail. The possibility of in-situ generation of NiCl2(DME) or α-chloroboronate to undergo coupling was ruled out based on control experiments (Scheme [23]A). After systematic mechanistic investigations, it was found that TBAC could reduce the potential of nickel catalysts, thereby accelerating the catalytic cycle. This conclusion was further supported by the results of cyclic voltammetry analysis. In combination with stoichiometric experiments and density functional theory (DFT) computational studies, a reasonable catalytic cycle was proposed (Scheme [23]B).

Zoom Image
Scheme 23 Mechanistic studies on nickel-catalyzed asymmetric coupling of perfluoroalkyl-substituted α-iodoboronates with aryl halides

With the success of NiH catalysis, the asymmetric coupling of α-haloboronic esters with alkenes was also studied. A preliminary result was given by Martin and co-workers, whereby an unactivated olefin was used; however, only 30% ee was obtained (Scheme [24]A).[25b] In 2021, the Fu and Lu group reported a reductive hydroalkylation of enamides wherein α-iodoboronates were utilized as the alkyl source (Scheme [24]B).[5d] Although moderate diastereoselectivities on the carbon adjacent to the B-atom (69) were given, these two diastereoisomers could be prepared in a single reaction and then separated through column chromatography. With this transformation, a wide array of chiral amino alcohols with high ee values can be readily obtained after simple oxidation of the products.

Zoom Image
Scheme 24 Ni-catalyzed asymmetric coupling of α-haloboronic esters with alkenes
Zoom Image
Scheme 25 Ni/photoredox-catalyzed enantioselective C(sp3)–C(sp3) reductive cross-electrophile coupling of unactivated alkyl halides with α-chloroboronates
Zoom Image
Scheme 26 The application of Ni/photoredox-catalyzed asymmetric reductive coupling of unactivated alkyl halides with α-chloroboronates in organic synthesis

Very recently, to further expand the application of α-haloboronates, we developed an enantioselective C(sp3)–C(sp3) reductive cross-electrophile coupling of unactivated alkyl ­halides with α-chloroboronates via dual nickel/photoredox catalysis (Scheme [25]A).[28] This is the first example of asymmetric reductive coupling of two different alkyl halides with nickel catalyst. Traditional reductants were not competent for this transformation (Scheme [25]B). Because organometallic reagents are not involved, many candidates with various functional groups can be employed in this coupling to deliver the products in excellent enantioselectivities and good to high yields.

The mild conditions enable a fast and facile method to construct chiral carbon centers, as shown in the synthesis of substrates 73 and 77, which needed many steps in previous work. With this method, they can be obtained in only two or three steps from α-chloroboronates (Scheme [26]). Furthermore, considering α-chloroboronates can be smoothly obtained from aldehydes by our developed methods, this protocol also has high practical value and step-economy in organic synthesis.

Zoom Image
Scheme 27 Mechanistic studies of Ni/photoredox-catalyzed asymmetric reductive coupling of unactivated alkyl halides with α-chloroboronates

Moreover, the mechanism was also investigated. As the coupling with aryl halides, the more active substrates α-bromo or iodoboronates were not suitable for this reaction (Scheme [27]A). These results reveal the importance of synchronous reaction rates of two electrophiles, especially in this C(sp3)–C(sp3) coupling. In addition, radical probe experiments proved that radical species were generated in both partners (Scheme [27]B). Further detailed studies illustrated that an out-of-cage radical was formed from the alkyl iodide, and a cage-rebound radical mechanism was presumably involved. Furthermore, the experiments with stoichiometric nickel catalyst supported the conclusion that the oxidative addition process via Ni(I) species, rather than the common Ni(0) catalyst. A proposed catalytic cycle was given based on these results (Scheme [27]C).

Just recently, the Fu group realized an asymmetric coupling of primary amides with racemic α-chloroboronic esters using a copper catalyst, and they synthesized a series of chiral secondary amides (Scheme [28]).[29] The product can be hydrolyzed to chiral secondary amines in the presence of hydrochloric acid, providing the possibility of obtaining chiral amino alcohols subsequently.

Zoom Image
Scheme 28 The copper-catalyzed asymmetric coupling of primary amides with racemic α-chloroboronic esters

# 4

Conclusion

Since the development of the Matteson homologation reaction in 1963, the preparation and transformation of α-haloboron compounds have always been important and attractive research fields. In the past decades, several novel conversions have been disclosed, especially in combination with transition-metal-catalysis chemistry. To date, the synthesis of these compounds has achieved several revolutionary advances. Many simple synthetic routes with good functional group compatibility have been reported, which provide suitable methods for their downstream investigations. However, in contrast, advances in the asymmetric transformation of racemic α-haloboron compounds have been much more limited, although rapid progress in the stereospecific transformation from chiral α-haloborons has been made. Therefore, the authors expect more elegant and useful advances in this field in the future.


#
#

Conflict of Interest

The authors declare no conflict of interest.


Corresponding Author

Tao XU
Shanghai Key Laboratory of Chemical Assessment and Sustainability, School of Chemical Science and Engineering, Tongji University
Shanghai 200092
P. R. of China   

Publication History

Received: 08 February 2023

Accepted after revision: 15 February 2023

Accepted Manuscript online:
15 February 2023

Article published online:
15 March 2023

© 2023. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany


   Permissions and Reprints All articles of this category
Zoom Image
Zoom Image
Zoom Image
Scheme 1 Matteson homologation reaction to α-chloroboron compounds
Zoom Image
Scheme 2 The preparation of α-bromoboron compounds with Schwartz’s reagent
Zoom Image
Scheme 3 Hydroboration of 1-halo-1-alkenes with catecholborane
Zoom Image
Scheme 4 The preparation of α-chloroboron compounds with dichloromethylboronate
Zoom Image
Scheme 5 The preparation of chiral α-haloboron compounds via hydrogenation of (1-chloro-1-alkenyl)boronic esters
Zoom Image
Scheme 6 The preparation of α-halo-β-carbonyl boronates via oxidative difunctionalization of alkenyl MIDA boronates
Zoom Image
Scheme 7 The preparation of α-bromo-β-carbonyl boron compounds via bromohydroxylation
Zoom Image
Scheme 8 Halohydroxylation and iodofluorination of alkenyl MIDA boronates
Zoom Image
Scheme 9 The preparation of α-haloboron compounds via photochemical radical C–H halogenation of benzyl MIDA boronates
Zoom Image
Scheme 10 The preparation of α-haloboron compounds via atom-transfer radical addition
Zoom Image
Scheme 11 The preparation of chiral α-haloboron compounds via nickel-catalyzed carbozincation of vinylboronic esters
Zoom Image
Scheme 12 The preparation of chiral α-chloroboronates via enantioselective catalytic 1,2-boronate rearrangement
Zoom Image
Scheme 13 The preparation of β-aryl-α-chloroboronates
Zoom Image
Scheme 14 The preparation of α-haloboronates via deoxygenative difunctionalization of carbonyls
Zoom Image
Scheme 15 The preparation of secondary α-haloboronates from aldehydes
Zoom Image
Scheme 16 The preparation of tertiary α-haloboronates from ketones
Zoom Image
Scheme 17 The preparation of chiral secondary and tertiary α-chloroboronates
Zoom Image
Scheme 18 Coupling with alkylzinc reagents to access chiral secondary boronic esters and applications of the method to homologation processes
Zoom Image
Scheme 19 An example of asymmetric reductive coupling of α-bromoboronic ester with aryl iodide
Zoom Image
Scheme 20 The Ni/photoredox-catalyzed asymmetric reductive coupling of α-chloroboronates with aryl halides
Zoom Image
Scheme 22 The nickel-catalyzed asymmetric coupling of perfluoroalkyl-substituted α-iodoboronates with aryl halides
Zoom Image
Scheme 21 Mechanistic studies on Ni/photoredox-catalyzed asymmetric reductive coupling of α-chloroboronates with aryl halides
Zoom Image
Scheme 23 Mechanistic studies on nickel-catalyzed asymmetric coupling of perfluoroalkyl-substituted α-iodoboronates with aryl halides
Zoom Image
Scheme 24 Ni-catalyzed asymmetric coupling of α-haloboronic esters with alkenes
Zoom Image
Scheme 25 Ni/photoredox-catalyzed enantioselective C(sp3)–C(sp3) reductive cross-electrophile coupling of unactivated alkyl halides with α-chloroboronates
Zoom Image
Scheme 26 The application of Ni/photoredox-catalyzed asymmetric reductive coupling of unactivated alkyl halides with α-chloroboronates in organic synthesis
Zoom Image
Scheme 27 Mechanistic studies of Ni/photoredox-catalyzed asymmetric reductive coupling of unactivated alkyl halides with α-chloroboronates
Zoom Image
Scheme 28 The copper-catalyzed asymmetric coupling of primary amides with racemic α-chloroboronic esters