7,10-Dibromo-2,3-dicyanopyrazinophenanthrene Aggregates as a Photosensitizer for Nickel-Catalyzed Aryl Esterification

Abstract

Self-assembled aggregates of 7,10-dibromo-2,3-dicyanopyrazinophenanthrene which act as a new organophotocatalyst in combination with Ni catalyst for the C_aryl–O_acyl cross-coupling reactions of carboxylic acids with aryl halides are described. This visible-light-induced C_aryl–O_acyl bond-formation reaction proceeds smoothly to afford aryl esters with satisfactory to excellent yields.

Aryl esters are important structural motifs present in various natural products, pharmaceuticals, agrochemicals, and polymers.[1] Therefore, the development of efficient methods for the synthesis of aryl esters has attracted considerable attention. The traditional method for the synthesis of aryl esters is the condensation of phenols with carboxylic acids or their derivatives.[2] Over the past years, transition-metal-catalyzed C_aryl–O_acyl cross-coupling reactions have become an important method for the synthesis of aryl esters, which include the Cu-catalyzed cross-coupling reactions of carboxylic acids with aryl-substituted trimethoxysilanes,[3] aryl halides,[4] aryl boronic acids,[5] and diaryliodonium salts;[6] Pd-catalyzed cross-coupling reactions of carboxylic acids with aryl halides;[7] and Rh-,[8] Pd-,[9] Ru-,[10] Co-,[11] or Cu[12]-catalyzed directing-group-assisted C–H activations with carboxylic acids. These methods are undoubtedly effective but suffer from drawbacks, such as requiring microwave radiation, high-temperature conditions, and use of expensive and/or noncommercially available starting materials. The visible-light-driven C_aryl–O_acyl bond formation is of great interest as an alternative route for the synthesis of aryl esters because visible light is a clean and abundant energy source. In 2017, MacMillan’s group developed the Ni(II)-catalyzed cross-coupling of carboxylic acids with aryl bromides promoted by Ir(ppy)₃ as a photocatalyst via energy transfer.[13] Recently, other organic photosensitizers, such as 1,2-dicyano-3,4,5,6-tetrakis(diphenylamino)-benzene (4DPAPN),[14] thioxanthen-9-one (TXO),[15] and boron-dipyrromethene (BODIPY),[16] have been successfully applied in Ni(II)-catalyzed C_aryl–O_acyl cross-coupling reactions (Scheme [1], previous work).

Recently, we reported 2,3-dicyanopyrazino phenanthrene (DCPP1) aggregates photocatalyst in visible-light-induced decarboxylative C–C cross-coupling reactions.[17] In the course of continuing research on (DCPP1) _n aggregates, we found that 7,10-dibromo-2,3-dicyanopyrazinophenanthrene (DCPP2) aggregates can be a photocatalyst to drive Ni-catalyzed cross-coupling of carboxylic acids with aryl halides (Scheme [1], this work). We herein report this result.

Initially, the C_aryl–O_acyl cross-coupling reaction of benzoic acid (1a) and 4-iodobenzoate (2a) was selected as a model reaction to optimize reaction conditions. Results are summarized in Table [1]. Thus, to a solution of 1a (0.3 mmol) and 2a (0.2 mmol) in DMF were added with the DCPP1 (5 mol%, equivalent concentration, 3·10^–3 M), NiCl₂·glyme (10 mol%), 4,4′-di-tert-butyl-2,2′-dipyridyl (dtbbpy, 10 mol%), and Cs₂CO₃ (0.3 mmol) under N₂ atmosphere, and the mixture was stirred at 40 °C for 24 h under 10 W 430 nm blue LED irradiation. The desired product p-carbomethoxyphenyl benzoate (3a) was obtained in 55% yield (entry 1).

Table 1 Optimization of Esterification between Benzoic Acid and Methyl 4-Iodobenzoate^a

Entry	PC	Base	Wavelength (nm)	Yield (%)b
1	DCPP1	Cs 2 CO 3	430	55
2	DCPP2	Cs 2 CO 3	430	75
3	DCPP3	Cs 2 CO 3	430	46
4	DCPP2	Na 2 CO 3	430	7
5	DCPP2	CsOAc	430	6
6	DCPP2	K3PO4	430	72
7	DCPP2	DBU	430	56
8	DCPP2	DMAP	430	13
9	DCPP2	Et3N	430	5
10	DCPP2	DIPA	430	76
11	DCPP2	BIPA	430	80
12c	DCPP2	BIPA	430	90
13	DCPP2	Cs 2 CO 3	400	43
14	DCPP2	Cs 2 CO 3	450	57

^a Standard conditions: 1a (0.3 mmol), 2a (0.2 mmol), photocatalyst (5 mol%), NiCl₂·glyme (10 mol%), ligand (10 mol%), base (1.5 equiv), solvent (3 mL), 40 °C, 10 W 430 nm blue LED irradiation for 24 h.

^b Isolated yield.

^c BIPA (3.0 equiv) was used.

When DCPP2 was used instead of DCPP1 as a photocatalyst, the yield of 3a was increased to 75% (entry 2). However, the yield of 3a was decreased to 46% by replacing DCPP1 with DCPP3 (entry 3). The base was subsequently screened using DCPP2 as photocatalyst. Among the bases tested (i.e., Cs₂CO₃, Na₂CO₃, CsOAc, K₃PO₄, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 4-dimethylaminopyridine (DMAP), Et₃N, diisopropylamine (DIPA), and N-tert-butylisopropylamine (BIPA)), the highest yield was obtained by using BIPA as base (entry 11 vs entries 2 and 4–10). When the amount of BIPA was increased to 3 equiv, the yield of 3a was improved to 90% (entry 12). Among the wavelengths tested (i.e., 400, 430, and 450 nm), the highest yield was obtained using a 430 nm LED light source (entries 12–14). Therefore, the subsequent C–O cross-coupling of carboxylic acids 1 with aryl halides 2 were carried by 5 mol% DCPP2, 10 mol% NiCl₂·glyme, 10 mol% dtbbpy, and 3.0 equiv BIPA in DMF at 40 °C for 24 h under 10 W 430 nm blue LED irradiation.

With the optimal conditions in hand, the substrate scope for carboxylic acids was first examined. Results are summarized in Scheme [2].[18] The reactions of aryl iodide substrates 1b–d, having a methyl group on the benzene ring at the ortho, meta, and para positions, respectively, afforded the corresponding products 3b–d in high yields (88–92%). These results indicate that the steric effect of the substituent linked on the benzene ring did not influence the reactivity of benzoic acid substrates. The yields of the products 3b–d slightly decreased when aryl iodide substrates were replaced by aryl bromides, indicating that the reaction activity of aryl iodides is higher than that of aryl bromides. However, aryl chlorides were not suitable for the present method. Benzoic acids bearing electron-donating groups (t-Bu and OMe) on the para position of benzene rings afforded the corresponding desired products 3e and 3f in 90% and 91% yields, respectively. By contrast, relatively low yield was observed in the reactions of 1i containing an electron-withdrawing group (CO₂Me) on the benzene ring. It is noteworthy that the reaction of substrate 1h bearing the OH group on the benzene ring resulted in 80% yield of 3h. This type of phenolic compound should be difficult to prepare by traditional condensation reactions with phenols. This transformation also tolerated benzoic acids with halogen functional groups fluoro (1j), chloro (1k), and bromo (1l) to afford products 3j–l in good yields. Moreover, the reaction worked well for primary, secondary, and tertiary alkyl carboxylic acids, such as acetic acid (1m), cyclohexanecarboxylic acid (1n), N-(tert-butoxycarbonyl)-proline (1o), and 1-adamantanecarboxylic acid (1p), delivering the corresponding products in moderate to high yields (3m–p, 75–91%). In addition, heteroaryl carboxylic acids, including 2-furoic acid (1q) and 2-thiophenecarboxylic acid (1r), were also suitable for the present method to afford the corresponding products 3q and 3r in 83% and 81% yields, respectively.

Next, the scope of aryl halides was explored in Scheme [3]. The reaction is compatible with various functional groups, including ester (2b and 2h), nitrile (2c), ketone (2d), aldehyde (2e), and trifluoromethyl (2f and 2g), and the corresponding esterification products 3b′–h′ were formed in 63–90% yields. This transformation also tolerated aryl iodides with halogen functional groups chloro (2i) and bromo (2j) to afford the products 3i′ and 3j′ in satisfactory yields.

After the successful development of the desired transformations, we focused on characterizing the [DCPP2] _n aggregates. The single-crystal X-ray diffraction analysis of DCPP2 shows that adjacent molecules are in proximity, thereby allowing π–π-stacking interactions (Figure S2). The crystallographically independent DCPP2 molecules are almost parallel to each other with molecules arranged in an antiparallel fashion between benzene rings at the distance of 3.5947 Å (Figure [1a]). UV/Vis absorption spectroscopy showed that DCPP2 (10^–5 M) had almost no absorption in the visible-light region. The spectrum of DCPP2 broadened to visible-light region at a concentration of 10^–3 M in DMF (Figure [1b]); the extent might be caused by the formation of aggregates at high material concentration. Next, the emission spectra of DCPP2 at different concentrations in DMF were examined to further prove the in situ formation of [DCPP2] _n aggregates. As shown in Figure [1c], the emission intensity of DCPP2 at 475 nm initially increased in the sample concentration from 1·10^–5 M to 1·10^–4 M and decreased dramatically at the concentration of 2·10^–4 M. The emission quenching is ascribed to the in situ formation of aggregates through physical π–π stacking at high concentrations in DMF.[19] Scanning electron microscopy (SEM) provided direct evidence for [DCPP2] _n aggregates formation (Figure [1d]).

As shown in Figure [2a], cyclic voltammogram measurements showed that the reductive potentials (E _1/2 ^red [DCPP1–3] _n ^•−/[DCPP1–3] _n = –1.79, –1.66, and –1.67 V vs SCE in DMF) are enough for the reduction of Ni^I into Ni⁰ (E _1/2 ^red [Ni^II/Ni⁰] = –1.2 V vs SCE in DMF).[20] The corresponding excited-state reductive potentials (E _1/2 ^red [DCPP1–3] _n ^*/[DCPP1–3] _n ^•−) are estimated to be +1.05, +1.24, and +1.32 V vs SCE.[21] These results show that the oxidation of the Ni^II complex II (E[Ni^II/Ni^III] = +1.0 V vs SCE in DMF)[21] by the [DCPP1] _n photocatalyst (E _1/2 ^red ([DCPP1] _n ^*/[DCPP1] _n ^•− = +1.05 V vs SCE in DMF) is unfavorable. However, the use of [DCPP1] _n as a photocatalyst provides a better result than that of [DCPP3] _n in previous screening of reaction conditions (55% vs 46%, Table [1], entries 1 and 3). Therefore, the present method may not undergo electron transfer. Moreover, an extensive region of overlap exists between the emission of [DCPP2] _n with the absorbance of Ni-A (Figure [2b]). In order to further prove the energy-transfer process, the reaction using 9-fluorenone (FLN) as a photocatalyst was carried out and the desired product 3a was obtained in 18% yield. The oxidation of the Ni^II complex II (E[Ni^II/Ni^III] = +1.0 V vs SCE in DMF) by FLN photocatalyst (E _1/2 ^red [FLN ^*/FLN ^•−] = +0.96 V vs SCE in DMF) is unfavorable. However, the triplet energy for 2.31 eV of FLN is thermodynamically capable to accelerate ester formation, since the triplet sensitization of Ni^II complex II requires an E _T of >1.85 eV.[22] These results suggest that the present method undergoes an energy-transfer process.

Based on our experimental outcomes and previous reports, a plausible reaction mechanism is depicted in Scheme [4]. The oxidative addition of the Ni(0) catalyst with ArI generates the Ni(II) complex I. The anion exchange of I with the carboxylate nucleophile forms aryl–Ni(II) carboxylate species II. Meanwhile, irradiation of the [DCPP2] _n photocatalyst with 430 nm blue LEDs generated the excited [DCPP2] _n ^*. At this juncture, energy transfer can occur between [DCPP2] _n ^* and aryl–Ni(II) species II, generating the excited aryl–Ni(II) species III while regenerating the ground state of [DCPP2] _n . Finally, the reductive elimination of III produces the esterification product and regenerates the Ni(0) species, thus completing the catalytic cycle.

In order to explore the practical utility of this method, a gram-scale experiment of 1a (9 mmol) with 2a (6 mmol) was carried out (Scheme [5]). After irradiation for 72 h under 36 W blue LED, the desired esterification product 3a was obtained in 75% yield (1.15 g).

In conclusion, we have developed a new type of [DCPP2] _n aggregates photoredox catalyst that was built through the π–π stacking of DCPP2 single molecule. The use of [DCPP2] _n aggregates as a visible-light photocatalyst in combination with Ni catalyst for C–O cross-coupling reactions of carboxylic acids with aryl halides was carried out to provide aryl esters in moderate to good yields. In contrast to Ru complexes, Ir complexes, and D–π–A dyes, the in situ formation of [DCPP2] _n aggregates in a certain concentration of organic solvent through physical π–π stacking will have great potential in organic synthesis. Further investigations on [DCPP2] _n aggregates in visible-light photocatalytic reactions are ongoing.

Conflict of Interest

The authors declare no conflict of interest.

• References and Notes

• 1a Fujiwara K, Sato T, Sano Y, Norikura T, Katoono R, Suzuki T, Matsue H. J. Org. Chem. 2012; 77: 5161
  CrossrefPubMedSearch in Google Scholar
• 1b Klare JE, Tulevski GS, Sugo K, de Picciotto A, White KA, Nuckolls C. J. Am. Chem. Soc. 2003; 125: 6030
  CrossrefPubMedSearch in Google Scholar
• 1c Schmidt JM, Tremblay GB, Pagé M, Mercure J, Feher M, Dunn-Dufault R, Peter MG, Redden PR. J. Med. Chem. 2003; 46: 1289
  CrossrefPubMedSearch in Google Scholar
• 1d Reddy MV. R, Rao MR, Rhodes D, Hansen MS. T, Rubins K, Bushman FD, Venkateswarlu Y, Faulkner DJ. J. Med. Chem. 1999; 42: 1901
  CrossrefPubMedSearch in Google Scholar
• 1e Pion F, Ducrot P.-H, Allais F. Macromol. Chem. Phys. 2014; 215: 431
  CrossrefSearch in Google Scholar
• 2a Chakraborti AK, Shivani S. J. Org. Chem. 2006; 71: 5785
  CrossrefPubMedSearch in Google Scholar
• 2b Ishihara K. Tetrahedron 2009; 65: 1085
  CrossrefSearch in Google Scholar
• 2c Carle MS, Shimokura GK, Murphy GK. Eur. J. Org. Chem. 2016; 23: 3930
  CrossrefSearch in Google Scholar
• 2d Otera J. Chem. Rev. 1993; 93: 1449
  CrossrefSearch in Google Scholar
• 3 Luo F, Pan CD, Qian PC, Cheng J. Synthesis 2010; 2005
• 4 Thasana N, Worayuthakarn R, Kradanrat P, Hohn E, Young L, Ruchirawat S. J. Org. Chem. 2007; 72: 9379
  CrossrefPubMedSearch in Google Scholar
• 5a Dai JJ, Liu JH, Luo DF, Liu L. Chem. Commun. 2011; 47: 677
  CrossrefPubMedSearch in Google Scholar
• 5b Zhang L, Zhang G, Zhang M, Cheng J. J. Org. Chem. 2010; 75: 7472
  CrossrefPubMedSearch in Google Scholar
• 6a Xie H, Yang S, Zhang C, Ding M, Liu M, Guo J, Zhang F. J. Org. Chem. 2017; 82: 5250
  CrossrefPubMedSearch in Google Scholar
• 6b Bhattarai B, Tay JH, Nagorny P. Chem. Commun. 2015; 51: 5398
  CrossrefPubMedSearch in Google Scholar
• 7a Kitano H, Ito H, Itami K. Org. Lett. 2018; 20: 2428
  CrossrefPubMedSearch in Google Scholar
• 7b Liang JY, Shen SJ, Xu XH, Fu YL. Org. Lett. 2018; 20: 6627
  CrossrefPubMedSearch in Google Scholar
• 8 Colby DA, Bergman RG, Ellman JA. Chem. Rev. 2010; 110: 624
  CrossrefPubMedSearch in Google Scholar
• 9a Krylov IB, Vil VA, Terent’ev AO. Beilstein J. Org. Chem. 2015; 11: 92
  CrossrefPubMedSearch in Google Scholar
• 9b Moghimi S, Mahdavi M, Shafiee A, Foroumadi A. Eur. J. Org. Chem. 2016; 3282
  Crossref
• 10 Padala K, Jeganmohan M. Chem. Commun. 2013; 49: 9651
  CrossrefPubMedSearch in Google Scholar
• 11a Lan J, Xie H, Lu X, Deng Y, Jiang H, Zeng W. Org. Lett. 2017; 19: 4279
  CrossrefPubMedSearch in Google Scholar
• 11b Lin C, Chen Z, Liu Z, Zhang Y. Adv. Synth. Catal. 2018; 360: 519
  CrossrefSearch in Google Scholar
• 11c Ueno R, Natsui S, Chatani N. Org. Lett. 2018; 20: 1062
  CrossrefPubMedSearch in Google Scholar
• 12 Wang F, Hu Q, Shu C, Lin Z, Min D, Shi T, Zhang W. Org. Lett. 2017; 19: 3636
  CrossrefPubMedSearch in Google Scholar
• 13 Welin ER, Le C, Arias-Rotondo DM, McCusker JK, MacMillan DW. C. Science 2017; 355: 380
  CrossrefPubMedSearch in Google Scholar
• 14 Lu J, Pattengale B, Liu Q, Yang S, Shi W, Li S, Huang J, Zhang J. J. Am. Chem. Soc. 2018; 140: 13719
  CrossrefPubMedSearch in Google Scholar
• 15 Zhu DL, Li HX, Xu ZM, Li HY, Young DJ, Lang JP. Org. Chem. Front. 2019; 6: 2353
  CrossrefPubMedSearch in Google Scholar
• 16 Zu W, Day C, Wei L, Jia X, Xu L. Chem. Commun. 2020; 56: 8273
  CrossrefPubMedSearch in Google Scholar
• 17 He M, Yu X, Wang Y, Li F, Bao M. J. Org. Chem. 2021; 86: 5016
  CrossrefPubMedSearch in Google Scholar
• 18 p-Carbomethoxyphenyl p-tert-Butylbenzoate (3e); Typical Procedure To a dried 20 mL reaction tube was charged with 4-(tert-butyl)benzoic acid (1e, 35.7 mg, 0.3 mmol), 4-iodobenzoate (2a, 52.4 mg, 0.2 mmol), DCPP2 (4.4 mg, 5 mol%), nickel(II) chlorine·diglyme (4.4 mg, 10 mol%), and dtbbpy (5.4 mg, 10 mol%). The tube was capped. After evacuated and backfilled nitrogen three times, DMF (3 mL) was added via a gastight syringe, followed by the addition of N-tert-butyl-isopropylamine (95 μL, 0.6 mmol). The reaction mixture was stirred under the irradiation of a 10 W 430 nm blue LED at 40 °C for 24 h. After 24 h, the mixture was quenched with water and extracted with ethyl acetate (3 × 10 mL). The combined organic layers were dried over Na₂SO₄ and concentrated under vacuo. The residue was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1: 5) to afford a white solid (56.5 mg, 90%); mp 115–117 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.14–8.11 (m, 4 H), 7.55–7.53 (m, 2 H), 7.31–7.28 (m, 2 H), 3.93 (s, 3 H), 1.37 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 166.4, 164.6, 157.8, 154.7, 131.2, 130.1, 127.6, 126.3, 125.7, 121.8, 52.2, 35.2, 31.1. IR: ν = 3422, 3134, 1639, 1400, 1122, 1035, 962, 601, 561 cm^–1. HRMS (ESI): m/z calcd [M + H]⁺: 313.1440; found: 313.1436.
• 19a Kumar GR, Sarkar SK, Thilagar P. Chemistry 2016; 22: 17215
  CrossrefPubMedSearch in Google Scholar
• 19b Reckmeier CJ, Schneider J, Xiong Y, Häusler J, Kasák P, Schnick W, Rogach AL. Chem. Mater. 2017; 29: 10352
  CrossrefSearch in Google Scholar
• 20a Terrett JA, Cuthbertson JD, Shurtleff VW, MacMillan DW. Nature 2015; 524: 330
  CrossrefPubMedSearch in Google Scholar
• 20b Perry IB, Brewer TF, Sarver PJ, Schultz DM, DiRocco DA, MacMillan DW. C. Nature 2018; 560: 70
  CrossrefPubMedSearch in Google Scholar
• 21 The energy level of the lowest-lying excited state is determined by calculating the energy of the wavelength at which the substrate’s UV/Vis absorption and emission spectra overlap, E₀,₀ (DCPP2) = 2.98 eV. E_1/2 ^red([DCPP2] _n */[DCPP2] _n ^•−) = +1.32 V vs SCE in DMF.
• 22 Welin ER, Le C, Arias-Rotondo DM, McCusker JK, MacMillan DW. C. Science 2017; 355: 380
  CrossrefPubMedSearch in Google Scholar

Corresponding Author

Publication History

Received: 31 July 2021

Accepted after revision: 31 August 2021

Article published online:
22 September 2021

© 2021. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References and Notes

• 1a Fujiwara K, Sato T, Sano Y, Norikura T, Katoono R, Suzuki T, Matsue H. J. Org. Chem. 2012; 77: 5161
  CrossrefPubMedSearch in Google Scholar
• 1b Klare JE, Tulevski GS, Sugo K, de Picciotto A, White KA, Nuckolls C. J. Am. Chem. Soc. 2003; 125: 6030
  CrossrefPubMedSearch in Google Scholar
• 1c Schmidt JM, Tremblay GB, Pagé M, Mercure J, Feher M, Dunn-Dufault R, Peter MG, Redden PR. J. Med. Chem. 2003; 46: 1289
  CrossrefPubMedSearch in Google Scholar
• 1d Reddy MV. R, Rao MR, Rhodes D, Hansen MS. T, Rubins K, Bushman FD, Venkateswarlu Y, Faulkner DJ. J. Med. Chem. 1999; 42: 1901
  CrossrefPubMedSearch in Google Scholar
• 1e Pion F, Ducrot P.-H, Allais F. Macromol. Chem. Phys. 2014; 215: 431
  CrossrefSearch in Google Scholar
• 2a Chakraborti AK, Shivani S. J. Org. Chem. 2006; 71: 5785
  CrossrefPubMedSearch in Google Scholar
• 2b Ishihara K. Tetrahedron 2009; 65: 1085
  CrossrefSearch in Google Scholar
• 2c Carle MS, Shimokura GK, Murphy GK. Eur. J. Org. Chem. 2016; 23: 3930
  CrossrefSearch in Google Scholar
• 2d Otera J. Chem. Rev. 1993; 93: 1449
  CrossrefSearch in Google Scholar
• 3 Luo F, Pan CD, Qian PC, Cheng J. Synthesis 2010; 2005
• 4 Thasana N, Worayuthakarn R, Kradanrat P, Hohn E, Young L, Ruchirawat S. J. Org. Chem. 2007; 72: 9379
  CrossrefPubMedSearch in Google Scholar
• 5a Dai JJ, Liu JH, Luo DF, Liu L. Chem. Commun. 2011; 47: 677
  CrossrefPubMedSearch in Google Scholar
• 5b Zhang L, Zhang G, Zhang M, Cheng J. J. Org. Chem. 2010; 75: 7472
  CrossrefPubMedSearch in Google Scholar
• 6a Xie H, Yang S, Zhang C, Ding M, Liu M, Guo J, Zhang F. J. Org. Chem. 2017; 82: 5250
  CrossrefPubMedSearch in Google Scholar
• 6b Bhattarai B, Tay JH, Nagorny P. Chem. Commun. 2015; 51: 5398
  CrossrefPubMedSearch in Google Scholar
• 7a Kitano H, Ito H, Itami K. Org. Lett. 2018; 20: 2428
  CrossrefPubMedSearch in Google Scholar
• 7b Liang JY, Shen SJ, Xu XH, Fu YL. Org. Lett. 2018; 20: 6627
  CrossrefPubMedSearch in Google Scholar
• 8 Colby DA, Bergman RG, Ellman JA. Chem. Rev. 2010; 110: 624
  CrossrefPubMedSearch in Google Scholar
• 9a Krylov IB, Vil VA, Terent’ev AO. Beilstein J. Org. Chem. 2015; 11: 92
  CrossrefPubMedSearch in Google Scholar
• 9b Moghimi S, Mahdavi M, Shafiee A, Foroumadi A. Eur. J. Org. Chem. 2016; 3282
  Crossref
• 10 Padala K, Jeganmohan M. Chem. Commun. 2013; 49: 9651
  CrossrefPubMedSearch in Google Scholar
• 11a Lan J, Xie H, Lu X, Deng Y, Jiang H, Zeng W. Org. Lett. 2017; 19: 4279
  CrossrefPubMedSearch in Google Scholar
• 11b Lin C, Chen Z, Liu Z, Zhang Y. Adv. Synth. Catal. 2018; 360: 519
  CrossrefSearch in Google Scholar
• 11c Ueno R, Natsui S, Chatani N. Org. Lett. 2018; 20: 1062
  CrossrefPubMedSearch in Google Scholar
• 12 Wang F, Hu Q, Shu C, Lin Z, Min D, Shi T, Zhang W. Org. Lett. 2017; 19: 3636
  CrossrefPubMedSearch in Google Scholar
• 13 Welin ER, Le C, Arias-Rotondo DM, McCusker JK, MacMillan DW. C. Science 2017; 355: 380
  CrossrefPubMedSearch in Google Scholar
• 14 Lu J, Pattengale B, Liu Q, Yang S, Shi W, Li S, Huang J, Zhang J. J. Am. Chem. Soc. 2018; 140: 13719
  CrossrefPubMedSearch in Google Scholar
• 15 Zhu DL, Li HX, Xu ZM, Li HY, Young DJ, Lang JP. Org. Chem. Front. 2019; 6: 2353
  CrossrefPubMedSearch in Google Scholar
• 16 Zu W, Day C, Wei L, Jia X, Xu L. Chem. Commun. 2020; 56: 8273
  CrossrefPubMedSearch in Google Scholar
• 17 He M, Yu X, Wang Y, Li F, Bao M. J. Org. Chem. 2021; 86: 5016
  CrossrefPubMedSearch in Google Scholar
• 18 p-Carbomethoxyphenyl p-tert-Butylbenzoate (3e); Typical Procedure To a dried 20 mL reaction tube was charged with 4-(tert-butyl)benzoic acid (1e, 35.7 mg, 0.3 mmol), 4-iodobenzoate (2a, 52.4 mg, 0.2 mmol), DCPP2 (4.4 mg, 5 mol%), nickel(II) chlorine·diglyme (4.4 mg, 10 mol%), and dtbbpy (5.4 mg, 10 mol%). The tube was capped. After evacuated and backfilled nitrogen three times, DMF (3 mL) was added via a gastight syringe, followed by the addition of N-tert-butyl-isopropylamine (95 μL, 0.6 mmol). The reaction mixture was stirred under the irradiation of a 10 W 430 nm blue LED at 40 °C for 24 h. After 24 h, the mixture was quenched with water and extracted with ethyl acetate (3 × 10 mL). The combined organic layers were dried over Na₂SO₄ and concentrated under vacuo. The residue was purified by flash column chromatography on silica gel (ethyl acetate/petroleum ether = 1: 5) to afford a white solid (56.5 mg, 90%); mp 115–117 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.14–8.11 (m, 4 H), 7.55–7.53 (m, 2 H), 7.31–7.28 (m, 2 H), 3.93 (s, 3 H), 1.37 (s, 9 H). ¹³C NMR (100 MHz, CDCl₃): δ = 166.4, 164.6, 157.8, 154.7, 131.2, 130.1, 127.6, 126.3, 125.7, 121.8, 52.2, 35.2, 31.1. IR: ν = 3422, 3134, 1639, 1400, 1122, 1035, 962, 601, 561 cm^–1. HRMS (ESI): m/z calcd [M + H]⁺: 313.1440; found: 313.1436.
• 19a Kumar GR, Sarkar SK, Thilagar P. Chemistry 2016; 22: 17215
  CrossrefPubMedSearch in Google Scholar
• 19b Reckmeier CJ, Schneider J, Xiong Y, Häusler J, Kasák P, Schnick W, Rogach AL. Chem. Mater. 2017; 29: 10352
  CrossrefSearch in Google Scholar
• 20a Terrett JA, Cuthbertson JD, Shurtleff VW, MacMillan DW. Nature 2015; 524: 330
  CrossrefPubMedSearch in Google Scholar
• 20b Perry IB, Brewer TF, Sarver PJ, Schultz DM, DiRocco DA, MacMillan DW. C. Nature 2018; 560: 70
  CrossrefPubMedSearch in Google Scholar
• 21 The energy level of the lowest-lying excited state is determined by calculating the energy of the wavelength at which the substrate’s UV/Vis absorption and emission spectra overlap, E₀,₀ (DCPP2) = 2.98 eV. E_1/2 ^red([DCPP2] _n */[DCPP2] _n ^•−) = +1.32 V vs SCE in DMF.
• 22 Welin ER, Le C, Arias-Rotondo DM, McCusker JK, MacMillan DW. C. Science 2017; 355: 380
  CrossrefPubMedSearch in Google Scholar

• Supplementary Material