Synthesis of bicyclic imidazoles via [2 + 3] cycloaddition between nitriles and regioselectively generated α-imino gold carbene intermediates.

Yuanjing Xiao, Liming Zhang

Index: Org. Lett. 14(17) , 4662-5, (2012)

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Abstract

The cyclic α-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 AuCl(3) as the catalyst.