Decarboxylative photocatalytic transformations.

Photocatalytic decarboxylation of carboxylic acids or their redox active esters has become an important strategy in organic chemistry. Using catalytic amounts of metal-based or organic photocatalysts, normally under visible light irradiation, these substrates generate carbon centered radicals, which have been applied to a broad range of C-C and C-heteroatom bond forming reactions. Addition reaction to electron-deficient alkenes, hydroalkylation of unsaturated C-C bonds and addition to C-heteroatom multiple bonds have been extensively studied. Cross-coupling reactions such as arylation, alkylation, allylation, vinylation, alkynylation, acylation, cyanation and C-H functionalization reactions are also successfully performed. In the case of C-heteroatom bond forming reactions, C-halogen, C-oxygen, C-sulfur, C-nitrogen, C-phosphorus, C-boron and C-silicon are fundamental functionalization processes. Hydro- and deuterodecarboxylation reactions allow the substitution of the carboxylic group by a hydrogen or a deuterium atom regioselectively. Finally, decarboxylative elimination reactions, such as olefination reactions for the synthesis of alkenes and decarboxylative C-C bond cleavage of cyclic carboxylic acids, give 1,n-dicarbonyl compounds. These photoredox transformations, a renaissance in organic chemistry, starting from readily accessible carboxylic acids widely available in Nature and the pharma industry with a great structural diversity occur under mild and simple reaction conditions with excellent efficiency and clean energy input.