Pyrimido-1, 4-benzothiazines and -1, 4-benzothiazepines. II. Thermal and Photochemical Rearrangements of Pyrimido-1, 4-benzothiazine Sulfonium Ylides

Abstract

Thermolysis of pyrimido-1, 4-benzothiazine sulfonium ylides caused competitively [1, 2] and [1, 4] rearrangements, or β-elimination, depending upon the natures of the substituents in the ylide moiety. Ultraviolet irradiation of the methyl, ethyl and benzyl sulfonium ylides resulted exclusively in the [1, 2] rearrangement followed by ring expansion leading to pyrimido-1, 4-benzothiazepines. On the basis of some data, the reaction sequences of these rearrangements were discussed.