Unexpected outcome of the Zn(OTf)2-catalyzed arylhydrazination of alkanoyl propargylamines: Rapid entry into 1-(arylamino)imidazoles

Abstract

When attempting to extend the Zn(OTf)2-catalyzed hydrazination of propargylic amides (en route to Fischer indoles) to alkanoic propargylamides, it was discovered that after the initial hydrazination event, the respective N-anilinoimidazoles are obtained. The use of stoichiometric ZnCl2 as the promoter still gave the Fischer indole product. The unexpected reaction outcome was attributed to the overly high electrophilicity of the alkanoic carboxamide carbon atom.