A Phosphetane Catalyzes Deoxygenative Condensation of α‑Keto Esters and Carboxylic Acids via P^III/P^VO Redox Cycling

A small-ring phosphacycle is found to catalyze the deoxygenative condensation of α-keto esters and carboxylic acids. The reaction provides a chemoselective catalytic synthesis of α-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.