Photocycloaddition reactions of thioimides with alkynes

Abstract

Photochemical reaction between N-methyl(thiophthalimide) and diphenylethyne or hex-3-yne involves selective cycloaddition at the CS bond, and yields a spiro-thiete product. A related spiro-1,2-dithiole isolated from the reaction mixture may be formed during the work-up procedure. With bis-(alkythio)ethynes, both N-methyl(thiophthalimide) and N-methyl(dithiophthalimide) form α-alkythio α,β-unsaturated dithioesters; such 1 : 1 adducts are most readily explained on the basis of initial spiro-thiete formation.