Synthesis of Bicyclic Imidazoles via [2+3] Cycloaddition between Nitriles and Regioselectively Generated α-Imino Gold Carbene Intermediates

The cyclic alpha-imino gold carbene intermediate B is most likely generated in situ via regioselective nitrene transfer from an azido group to a tethered terminal alkyne in the presence of a gold catalyst and at ambient temperature. This highly electrophilic intermediate can react with a weakly nucleophilic nitrile, which is used as the reaction solvent, to deliver a bicyclic imidazole rapidly in an overall bimolecular [2 + 2 + 1] cycloaddition and in mostly serviceable yield. The competing intramolecular Huisgen reaction, although likely also catalyzed by gold, is minimized by using AuCl3 as the catalyst.