ON THE PHOTOISOMERIZATION OF THIOPHENE AND THIAZOLE DERIVATIVES

The photochemical isomerization of thienyl and thiazolyl derivatives can be explained by assuming the formation of the Dewar isomer. The isomerization of the Dewar isomer towards the most stable one can account for the observed reaction. No biradical intermediate was found. In the case of thiophene an isomerization of the Dewar thiophene allows the formation of a tricyclic intermediate; a retroelectrocyclic reaction can afford the reaction product. This tricyclic intermediate cannot be formed in the photoisomerization of thiazole derivative.