Photoinduced Decarboxylative Radical Phosphinylation

Reported herein is an unprecedented protocol for C(sp3)-phosphinylation. With 1 mol % 4CzIPN (1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene) as the catalyst, the visible light induced reaction of redox-active esters of aliphatic carboxylic acids with dimethyl arylphosphonites or diethyl alkylphosphonites at room temperature provides the corresponding decarboxylative phosphinylation products in satisfactory yields. The protocol exhibits broad substrate scope and wide functional-group compatibility, enabling the late-stage modification of complex molecules and rapid synthesis of bioactive phosphinic acids such as glutamine synthetase phosphinothricin and a kynureninase inhibitor. A radical-polar crossover mechanism involving the formation and subsequent oxidation of phosphoranyl radicals followed by nucleophilic demethylation (or deethylation) is proposed. Decarboxylative radical phosphinylation of N-acyloxyphthalimides with aryl- or alkylphosphonites has been accomplished under metal-free conditions. An unprecedented mechanism involving the formation and subsequent oxidation of phosphoranyl radicals is proposed.image