Mechanism of the photorearrangements of phenylthiazoles

Abstract

Various arylthiazoles have been subjected to photolysis. The resulting photorearrangements have been classified as type A or B. Type A involves formal exchange of positions 2 and 4, or 3 and 5. Type B involves formal interchange of positions 2 and 3 with concomitant inversion of positions 4 and 5. The mechanistic aspects of the reaction are discussed and we present a mechanism involving a tricyclic sulphonium cation and subsequent formation of a more stable bicyclic intermediate leading to the rearrangement product. Strong support for our proposed mechanism has been provided by deuterium incorporation during the rearrangement of 2-phenylthiazole (17) or 4-phenylthiazole (19) to 3-phenylisothiazole (18).