Synthesis of 1-aryl-1,3-diyne and 2-aryl-1,1-dialkynylethene from the Sonogashira reactions of 2-aryl-1,1-dibromoethene

Both 1-aryl-1,3-diyne and 2-aryl-1,1-dialkynylethene were produced from the Sonogashira reactions of 2-aryl-1,1-dibromoethene with 1-alkyne. The ratio of the products varied according to the reaction conditions. The coupling reactions in benzene afforded the 2-aryl-1,1-dialkynylethene as a major product and no 1-aryl-1,3-diyne was isolated. The 1-aryl-1,3-diyne could be obtained in DMF in acceptable yields. When amines were used as a reaction solvent, the coupling reaction gave the 2-aryl-1,1-dialkynylethene (20%) and the conjugated enyne (68%) in diisopropylamine, whereas only the 1-aryl-1,3-diyne was isolated in piperidine in 56% yield.