CIS-TRANS-ISOMERIZATION OF STYRYLPYRROLES BY STRAY LIGHT

A series of substituted N-methylstyrylpyrroles (H, p-Br, p-CN, o,p-diCl, m-CH3, m-CN, m-NO2) were prepared via the Wittig reaction of 1-methylpyrrole-2-carboxaldehyde and substituted benzyltriphenvlphosphonium bromides. Both cis and trans isomers were found to be present in the reaction mixture and they were separable by column chromatography in a few cases (H, p-Br, m-CN, m-NO2). Photochemical isomerizations of cis-styrylpyrroles to trans isomers were observed when the substituents were o,p-diCl and m-NO2, while the opposite was the case with compounds having H, p-Br, m-CH3, m-CN. It was difficult to separate the cis and trans mixture of p-cyanostyrylpyrroles and the equilibrium ratio did not change under similar photochemical reaction conditions.