Decarboxylative photocatalytic transformations

Abstract

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.