On the mechanism of CuCl mediated amine addition to diacetylenes

A mechanism of CuCl mediated amine addition to diacetylenes resulting in pyrrole formation has been studied theoretically at B3LYP/6-31G* level of theory. The reaction proceeds via formation of Cu-stabilized carbene intermediates and the formation of the first intermediate is the rate determining reaction step. The catalytic action of CuCl is due to the reduction of activation energy of the carbene intermediate formation from 75.0 to 50.1 kcal/mol. The decrease in activation energy is related to the reduction of HOMO-LUMO energy gap between nucleophile and electrophile due to complex formation allowing to catalogue this reaction as interaction between soft acid and base.