Visible-Light-Driven Thiolate-Catalyzed Carboxylation of C(sp2)–H Bonds in Azines with CO2

Catalytic carboxylation of C−H bonds with CO2 represents a sustainable and economic strategy to produce valuable carboxylic acids. However, it is highly challenging due to their low reactivities and selectivity issue. Although great progress has been achieved in this field, catalytic carboxylation of C−H bonds in azines (nitrogen-containing aromatic heterocycles), which are important and widely-existing, with CO2 is still challenging. Herein, we report a novel visible-light-driven thiolate-catalyzed carboxylation of C(sp2)−H bonds in azines with CO2. A variety of azines, such as quinolines, pyridines, phenanthroline, naphthyridine, and acridine, undergo such a catalytic carboxylation smoothly. This strategy also features high regioselectivity, mild and transition-metal-free reaction conditions, high step-, atom-, and redox-economy, good functional group tolerance as well as facile scalability. The utility of this method is demonstrated by efficient synthesis of bioactive molecules, such as cinchophen and brequinar derivatives, as well as precise modification of commonly-used N-ligands, including bipyridines, terpyridine and phenanthroline. Mechanistic investigations support the formation of electron donor-acceptor (EDA) complexes between thiolates and azines.