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 (1-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 °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 ¹³C additivity scheme and the chemical shifts are more closely predicted using known oxetanes of 1-X with methacrylonitrile. The product formation bias resulting from the attack on the syn-face can be explained using the Cieplak transition state theory.