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).