Visible-Light-Driven Carboxylative 1,2-Difunctionalization of C=C Bonds with Tetrabutylammonium Oxalate.

Herein, we report a visible-light-induced charge-transfer-complex-enabled dicarboxylation and deuterocarboxylation of C=C bonds with oxalate as a masked CO₂ source under catalyst-free conditions. In this reaction, we disclosed the first example that the tetrabutylammonium oxalate could be able to aggregate with aryl substrates via π-cation interactions to form the charge transfer complexes, which subsequently triggers the single electron transfer from the oxalic dianion to the ammonium countercation under irradiation of 450 nm bule LEDs, releasing CO₂ and CO₂ radical anions. Diverse alkenes, dienes, trienes, and indoles, including challenging trisubstituted olefins, underwent dicarboxylation and anti-Markovnikov deuterocarboxylation with high selectivity to access valuable 1,2- and 1,4-dicarboxylic acids as well as indoline-derived diacids and β-deuterocarboxylic acids under mild conditions. The in situ generated CO₂ ^•- and CO₂ molecules from oxalic radical anions could both add to the C=C bond without assistance of any photocatalyst or additives, which made this reaction sustainable, clean, and efficient.