Chloroformates, 1-alkyne coupling

Cross-coupling of terminal alkynes with aryl and vinyl halides are usually carried out in organic solvents, such as benzene, dimethylformamide or chloroform with a palladium-based catalyst and a base scavenger for the hydrogen halide. Copper(I) iodide is a particularly effective co-catalyst allowing the reaction to proceed under mild conditions. 

Henkelmann and co-workers found that chloroformates are good coupling partners of 1-alkynes, and the reaction offers a useful synthetic method for aryl-propiolates [87]. Reaction of n-butyl chloroformate with phenylacetylene in the presence of 1,2,2,6,6-pentamethylpiperidine as a hindered base and a small amount of A, A-dimethylaminopyridine afforded n-butyl phenylpropiolate (188) in 98% yield within 25 min in refluxing dichloromethane. 

Alkynic esters are prepared by the coupling of terminal alkynes with chlorofor-mate 157. Butyl chloroformate (157) is an unstable compound, and the reaction... 

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