Divergent Construction of Fully Substituted Pyrroles and Cyclopentadiene Derivatives by Ynamide Annulations: 1,2-Cyclopropyl Migration versus Proton Transfer

A switchable cyclopropyl ynamide cyclization to construct fully substituted pyrroles and cyclopentadiene derivatives in the presence of a gold catalyst was developed. In this version of pyrrole generation, a novel method to furnish gold vinylidenes through [1,2]-cyclopropyl migration was described. On the contrary, the production of cyclopentadienes proceeded through a proton-transfer step. These intriguing mechanisms were proposed based on the structure identification of the alkynyl enamine intermediate and a crossover experiment. The feasibility of cyclobutyl ynamides to specifically construct cyclopentadienes through ring expansion was also investigated.