Mechanism of Intramolecular Photocycloadditions of Cyclooctenones

Article abstract of DOI:10.1021/jo00392a020

The intramolecular photochemical <2+2> cycloadditions of a number of 4'-substituted (3'-butenyloxy)-cyclooctenones have been studied.Two classes of substrates were found.One class (phenyl- and vinyl-substituted) forms <2+2> adducts in an efficient reaction, while the rest of the compounds from photoproducts slowly and in low yield.The behavior of a carbon analogue shows that rotational relaxation of the cyclooctenone triplet is faster than <2+2> cycloaddition.Based on quenching and sensitization studies, it has been suggested that the substituent effect is indicative of an enhanced rate of cyclization to form a 1,4-biradical.