A Phosphetane Catalyzes Deoxygenative Condensation of α-Keto Esters and Carboxylic Acids via PIII/PV=O Redox Cycling

A small-ring phosphacycle is found to catalyze the deoxygenative condensation of alpha-keto esters and carboxylic acids. The reaction provides a chemoselective catalytic synthesis of alpha-acyloxy ester products with good functional group compatibility. Based on both stoichiometric and catalytic mechanistic experiments, the reaction is proposed to proceed via catalytic P-III/P-V-O cycling. The importance of ring strain in the phosphacyclic catalyst is substantiated by an observed temperature-dependent product selectivity effect. The results point to an inherent distinction in design criteria for organophosphorus-based catalysts operating via P-III/P-V-O redox cycling as opposed to Lewis base (nucleophilic) catalysis.