Unsymmetrical Coupling of 1-Chloroalkynes and Terminal Alkynes under ­Experimental Sonogashira Conditions

The coupling of a 1-chloroalkyne and a terminal alkyne to furnish a 1,3-butadiyne under experimental Sonogashira conditions is investigated. Through competition experiments, it is found that 1-chloroalkynes provide cross-coupling products as efficiently (or slightly better) in comparison with iodobenzenes, and almost as effectively as vinyl bromides. Yet, in regard to the degree of conversion into various products, chloroalkynes are the most reactive of all the substrates examined under the explored conditions. Optimized conditions for this cross-coupling reaction are presented.