[2-PHOTOCYCLOADDITION OF 2 CAPTODATIVE ALKENES TO 3-ACETYLTHIANAPHTHENE(2])

Photoexcited 3-acetylbenzo[b]thiophene (1c) adds 2-morpholinopropeneni trile (2a) in a [2 + 2] mode at the C-2-C-3 bond regioselectively but stereounselectively with formation of cyclobuta[b][1]benzothiophenes 3 a and 4a. In addition, the isomeric adduct 5 is formed from 2a and exc ited 2-acetylbenzo[b]thiophene (1b) accompanying 1c as an impurity. Si milarly, 2-(tert-butylthio)propenenitrile (2b) undergoes a smooth and highly regioselective but stereounselective [2 + 2] photoaddition to I c yielding a mixture of two isomeric adducts from which compound 3b ma y be separated by recrystallization. The configuration of 5 was unambi guously confirmed by an X-ray crystal structure analysis. The structur es of the other cycloadducts were derived by a comparison of their H-1 -NMR spectral data with those of closely related substances from other work.