Sequential Sonogashira and Glaser coupling reactions: facile access to 1,4-disubstituted 1,3-butadiynes from arylbromide

Abstract

A simplified synthesis of symmetrical 1,4-disubstitued 1,3-butadiynes was developed using a sequential two-step process combining a typical Sonogashira coupling with a Glaser coupling. The Sonogashira reaction coupled arylbromide and trimethylsilylacetylene. In the second step, a Glaser coupling reaction was performed using the crude trimethyl(arylethynyl)silane product from the previous Sonogashira coupling in a basic solvent; the Glaser coupling proceeded to completion without the addition of extra Pd or Cu catalysts. The catalytic amount of metal (Cu and Pd) in the second step was substantially less than that used in a typical Glaser coupling reaction.