Visible-light-driven synthesis of N-heteroaromatic carboxylic acids by thiolate-catalysed carboxylation of C( sp ²)–H bonds using CO 2

Catalytic carboxylation of C–H bonds using CO 2 is a sustainable and economic strategy to produce valuable carboxylic acids. However, this process presents challenges due to the low reactivity of C–H bonds and difficulties in controlling regioselectivity. Although progress has been made in this field, catalytic carboxylation of C–H bonds in azines with CO 2 is still a challenge. Here we report a visible-light-driven, thiolate-catalysed carboxylation of azine C( sp 2 )–H bonds using CO 2 . A variety of azines, including quinolines, pyridines, phenanthroline, naphthyridine and acridine, can undergo catalytic carboxylation to give N-heteroaromatic carboxylic acids in good yields and with excellent regiocontrol. This method operates under mild and transition-metal-free reaction conditions, is tolerant of a wide range of functional groups and is scalable. The utility of this method is demonstrated by application to the synthesis of bioactive molecules, such as cinchophen and brequinar derivatives, and to the modification of commonly used nitrogen ligands, including bipyridines, terpyridine and phenanthroline. Mechanistic investigations reveal the formation of an electron donor–acceptor complex between the thiolate catalyst and azine substrate.