Configuration and stereochemistry of photoproducts by application of the nuclear Overhauser effect. Adducts of benzophenone with methyl-substituted furans and 2,5-dimethylthiophen, and of methyl-substituted maleic anhydrides with thiophen and its methyl derivatives, and benzo-[b]thiophen

Abstract

The configurations and the stereochemistry of two series of photocycloaddition products have been elucidated by means of ¹H n.m.r. spectroscopy including intramolecular internuclear Overhauser effect measurements. The first series consists of the oxetans (3)–(6) obtained by photoreactions of benzophenone with 3- and 2-methylfuran (1a and b). furfuryl alcohol (1c), 2,3-dimethylfuran (1d), and 2,5-dimethylthiophen (1e). The second series includes photocycloaddition products (9)–(18) formed in reactions of methyl-substituted maleic anhydrides (8a and b) with thiophen (7a), methylthiophens (7b–d), and benzo[b] thiophen (15).