Face selectivity in the photocycloaddition reactions of acrylonitrile to 5-substituted adamantan-2-ones and pyrolysis of the products to methyleneadamantanes

Abstract

The photocycloaddition of acrylonitrile to 5-substituted adamantan-2-ones :(l-X) produces two geometrically isomeric oxetanes in which the oxygen atom and the 5-substituent are in the anti or syn positions, The substituent was varied from fluoro, chloro, bromo, hydroxy to phenyl and the product ratios were similar (ca, 60:40) in all instances, Small portions (<5%) of the oxetanes were pyrolysed when analysed by GC at above 200 degrees C, and the products from the pyrolysis were confirmed to be the corresponding methyleneadamantanes by independent syntheses, Assignment of the configuration of the oxetanes was found to be consistent with C-13 additivity scheme and the chemical shifts are more closely predicted using known oxetanes of l-X with methacrylonitrile. The product formation bias resulting from the attack on the syn-face can be explained using-the Cieplak transition state theory.