CO2 + Light: “Green” Valorization of Simple Arenes and Styrenes

Abstract

An innovative approach furnishing valuable molecules from simple precursors via C-H functionalization, photocatalysis as a sustainable activation mode, no metal catalyst, and CO 2 valorization: these are the salient features of the carboxylation of diverse arenes and styrenes developed by Bergonzini, Ko ¨nig, and co-workers in this issue of Chem.

Visible-Light-Induced Transition-Metal-Free Redox-Neutral Carboxylation of Remote Benzylic C(sp3)–H Bonds via 1,5-Hydrogen Atom Transfer

“…Carbon dioxide (CO 2 ) presents an ideal but challenging renewable single carbon (C1) synthetic block for organic synthesis. ,− Due to the inherent electrophilicity of CO 2 , researchers have successfully achieved carboxylation reactions of C­(sp)–H and C­(sp 2 )–H bonds in the presence of appropriate bases. ,,,− However, direct carboxylation of an unactivated C­(sp 3 )–H bond with CO 2 has rarely been reported. The relatively high stability of the benzylic carbon radical and its smooth reduction to carbanion enable an efficient attack on CO 2 for achieving carboxylation reactions; many researchers have focused their attention on the carboxylation of benzylic C­(sp 3 )–H bonds. , In 2015, Murakami’s group reported the direct carboxylation reactions of the benzylic C­(sp 3 )–H bond excited by ultraviolet light .…”

Photocarboxylation of remote C–H bonds through nitrogen-centred radical 1,5-hydrogen atom transfer

“…[37][38][39][40][41] Many researchers have made outstanding contributions to the carboxylation of different types of C-H bonds. [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] In this context, the generation of carbanions via visible-light photoredox catalysis, concomitant with the reduction of CO 2 for carboxylation purposes, has emerged as a prevalent methodology employed in photocarboxylation reactions. 43,45,46,49,54,57,58 He and co-workers have meticulously detailed recent work related to photocarboxylation reactions involving CO 2 in their comprehensive review.…”

“…[42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] In this context, the generation of carbanions via visible-light photoredox catalysis, concomitant with the reduction of CO 2 for carboxylation purposes, has emerged as a prevalent methodology employed in photocarboxylation reactions. 43,45,46,49,54,57,58 He and co-workers have meticulously detailed recent work related to photocarboxylation reactions involving CO 2 in their comprehensive review. 59,60 In 2015, Murakami and his colleagues disclosed a unique approach wherein ultraviolet light excitation (365 nm) was employed to amalgamate the 1,5-hydrogen atom transfer (HAT) process with carboxylation, offering new insights for the photocarboxylation of remote carbon-hydrogen bonds.…”