Pyrroles react with 1-acyl-2-bromoacetylenes at room temperature on silica to give 2-acyl-1,1-di(pyrrol-2-yl)ethenes as major products in yields of up to 60%. Under reaction conditions employed, the intermediates (E)-2-(2-acyl-1-bromoethenyl)pyrroles (3-11% isolated yields) either readily exchange the bromine atom for the pyrrole molecule or eliminate HBr to afford 2-(2-acylethynyl)pyrroles, which can be isolated in 9-22% yields by chromatography of the reaction mixture on Al2O3.
pyrroles - 1-acyl-2-bromoacetylenes - 2-(2-acyl-1-bromoethenyl)pyrroles - 2-acyl-1,1-di(pyrrol-2-yl)ethenes - 2-(2-acylethynyl)pyrroles - silica
