Tropolonate Salts as Acyl Transfer Catalysts for Esterification Reactions under Thermal and Photochemical Conditions

Acyl transfer catalysis is a frequently used tool to promote the formation of carboxylic acid derivatives, which are important synthetic precursors and target compounds in organic synthesis. However, there have been only a few structural motifs known to efficiently catalyze the acyl transfer reaction. Herein we introduce a new acyl transfer catalytic paradigm based on the tropolone framework. We show that tropolonate salts, due to their strong nucleophilicity and photochemical activity, can promote the coupling reaction between alcohols and carboxylic acid anhydrides or chlorides to give the products with excellent efficiency under thermal or blue light-photochemical conditions. Kinetic studies and density functional theory (DFT) calculations suggest interesting mechanistic insights for reactions promoted by this new acyl transfer catalytic system.