PHOTOCHEMICAL TRANSFORMATIONS OF SMALL RING CARBONYL COMPOUNDS .19. PHOTOCHEMISTRY OF BENZOYLCYCLOBUTANES

The photolysis in benzene of cyclobutyl phenyl ketone has been found to afford four products. The structures have been assigned as 1-phenyl-4-penten-1-one, 2-hydroxy-2-phenylbicyclo[1.1.1]pentane, cyclobutyl-phenylcarbinol, and the pinacol of starting material. The formation of the keto olefin and the bicyclopentanol is considered to proceed through a diradical intermediate formed by transannular hydrogen abstraction by the excited n-π* triplet. The inefficiency of the photoreaction, both in terms of quantum yield and rate, is attributed to the unfavorable geometry required for internal hydrogen transfer, cis- and trans-2-phenylcyclobutyl phenyl ketones undergo rapid photointerconversion followed by a further intramolecular reaction to produce 1,5-diphenyl-4-penten-1-one. The photoisomerization has been rationalized by homolytic ring cleavage of the cyclobutyl ring. © 1969, American Chemical Society. All rights reserved.