Insights into the mechanisms of Cu(i)-catalyzed heterocyclization of α-acyl-α-alkynyl ketene dithioacetals to form 3-cyanofurans: the roles of NH4OAc

Abstract

A computational study with the M06-2X/B3LYP density functional is carried out to explore the effects of NH₄OAc on the Cu(I)-catalyzed heterocyclization of α-acyl-α-alkynyl ketene dithioacetals to form 3-cyanofurans. The calculations suggest the following. (a) The use of CuBr as the catalyst decreases significantly the free energy barriers of intramolecular cyclization and intermolecular addition. (b) NH₄OAc can be decomposed into NH₃ and HOAc. NH₃ as the proton shuttle is critical in the stepwise H⁺-transport process because it can greatly reduce the rate-determining free energy barrier of whole Cu(I)-catalyzed reactions (from 251.1 to 130.1 kJ mol⁻¹). (c) HOAc also plays a role similar to that of NH₃ in the H⁺-transport reactions. These studies are expected to improve our understanding of transition-metal-catalyzed reactions and provide guidance for the future design of new catalysts and new reactions.