A Phosphetane Catalyzes Deoxygenative Condensation of α-Keto Esters and Carboxylic Acids via P~Ⅲ/P~Ⅴ=O Redox Cycling

摘要

A small-ring phosphacycle is found to catalyze the deoxygenative condensation of α-keto esters and carboxylic acids. The reaction provides a chemo-selective 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 organo-phosphorus-based catalysts operating via P~Ⅲ/P~Ⅴ=O redox cycling as opposed to Lewis base (nucleophilic) catalysis.