Photoreactions of 1,3-dihydroisobenzofuran-1-thiones and 1,3-dihydro-2-benzothiophene-1-thiones with alkenes

Abstract

The photoreactions of isobenzofuran-1-thiones 7 and 2-benzothiophene-1-thiones 11 in the presence of alkenes have been examined. Irradiation of thiones 7 and 11 in the presence of alkenes gave spiro-thietanes 15 and 21, which are formed by [2 + 2] cycloaddition of the CS bond of thiones and the CC bond of alkenes. The spiro-thietanes 15a, b, d and e, derived from 3-unsubstituted or 3-monosubstituted 1,3-dihydroisobenzofuran-1-thiones 7a, b, d and e and alkenes, are somewhat labile and undergo thermal rearrangement to give the tricyclic isobenzofurans 16. The formation of compounds 16 can be explained on the basis of ring-cleavage of the thietanes, assisted by the participation of the oxygen lone-pair electrons.