Rapid Access of Alkynyl and Alkenyl Coumarins via a Dipyridinium Methylide and Propargylamine Cascade Reaction.

Abstract

A DMAP-catalyzed cascade approach allowing facile assembly of alkynyl coumarins is reported. By virtue of reactive o-AQM (in situ generated from modular propargylamine) and a new synthetic equivalent of acyl carbene (from pyridinium ylide), the reaction proceeds smoothly to afford a variety of alkynyl coumarins in good-to-excellent yields. This transition-metal-free and oxidant-free process features moderate functional group tolerance, particularly the -Br group; thus, this protocol circumvents the inherent shortcomings of the existing Sonogashira coupling of coumarin triflates. This versatile method is also found to be applicable to the preparation of β-alkenyl coumarins, resembling the outcomes of the current Heck-type coupling reaction.