Aliphatic C–H arylation with heteroarenes without photocatalysts

Abstract

This work presents a scalable and mild strategy for aliphatic C–H arylation with heteroarenes under metal-free, photocatalyst-free and strong oxidant-free conditions.

Metal- and photosensitizer-free cross-dehydrogenative coupling through photoinduced energy transfer

“…Over the past few decades, the exploration of photocatalytic Minisci-type alkylation has seen significant progress with the advancement of photoredox catalysis. 4 Various sources of alkyl radicals, including alcohols, 5 aldehydes, 6 boronic acid, 7 carboxylic acids, 8 alkyl halides, 9 oxime esters 10 and redox active esters (RAEs), 11 have proven effective in generating alkylated N-heteroarenes through this low-energy consumption mode. On the other hand, direct alkyl radical generation through hydrogen atom abstraction from alkanes offers a highly atom- and step-efficient method, owing to the abundant availability of alkyl structures.…”

Merging Quinoxalin-2(1H)-ones Excitation with Cobaloxime Catalysis: C3 Alkylation of Quinoxalin-2(1H)-ones with Unactivated Alkyl Iodides and Carboxylic Acids under Light

“…We found that 1a* possesses good redox ability ( E ox * = −1.49 V vs Ag/AgCl, E red * = 1.73 V vs Ag/AgCl; for details, see Figures S6 and S7) to react with Et 3 N or alkyl acid via a SET process to yield carbon radicals. Besides, when irradiated by 395 nm LEDs, the EPR signal of cyclohexyl radical (α N = 14.6 G, α H = 21.6 G) was detected when injecting 1a and heptanaphthenic acid into CH 3 CN solution (Figure B). However, 1a emission quenching with Et 3 N, 2-phenylpropionic acid, and Co­(dmgH) 2 pyCl showed excited 1a strongly reacted with Co­(dmgH) 2 pyCl, resulting in the yield of 1a radical cation intermediate (Figure C–F).…”

“…For example, in 2021, the Li group found that various N -heterocycles could be successfully excited under >280 nm light irradiation and achieved the C­(sp 3 )–H bond heteroarylation by a hydrogen-atom transfer (HAT) process via a chlorine radical formed in situ . Recently, aliphatic C–H bonds also could be transferred into an alkyl radical intermediate in the presence of O 2 or TBHP . Herein, we propose excited quinoxalin-2­(1 H )-ones and combined cobaloxime catalysis to construct 3-alkylated products using carboxylic acids or alkyl iodides as alkylation regents without external strong acids, photocatalyst, or equivalent oxidants (Scheme C).…”

Visible-light-mediated direct C3 alkylation of quinoxalin-2(1H)-ones using alkanes

“…60–64 However, the approach of direct C–H functionalization of heteroarenes through the direct activation of alkanes remains to be an ongoing obstacle. 65–68…”