Cobalt catalyzed synthesis of α, β-unsaturated esters from esters and alcohols via mild O2-interrupted hydrogen borrowing

Abstract

The implementation of direct and mild catalytic synthesis of products from benign materials using inexpensive catalysts is a major goal of chemists. Herein, a mild O2-interrupted hydrogen borrowing strategy using easily accessible and high efficient cobalt complex was reported for direct synthesis of α, β-unsaturated esters from unactivated esters and alcohols. This new route had good tolerance on broad substrate scope (alcohols, acetates, propionates and dios) and functional group with the highest yield of 89.1%. Systematic mechanism investigation revealed the cobalt complex was activated by t-BuOK via double deprotonation of PN5P ligand and removal of dichloro ligands, followed by two-fold alcohols activation and dehydrogenation. Also, the oxygen atmosphere was demonstrated very crucial for such interrupted hydrogen borrowing pathway.