PHOTOCHEMISTRY OF DELTA-HYDROXYBUTYL ALPHA,BETA-UNSATURATED GAMMA,DELTA-EPOXY NITRILES, FORMATION OF SPIRO KETALS

Photocyclization reactions of delta-hydroxybutyl alpha,beta-unsaturate d gamma,delta-epoxy nitriles 4a, b at 254 nm lead to spiro ketals 5a, b and 6a, b arising from the carbonyl ylide intermediate A. The spiro ketal 6b containing an endocyclic double bond is transformed to spiro ether 16 by an acid-catalyzed 1,3-sigmatropic rearrangement. The ratio of spiro ketals 5 and 6 has been shown to depend on solvent polarity and acidity of additives. Application to the synthesis of pheromones i s presented. X-ray crystal structure analyses are performed on dispiro compound 18 and spiro ester 25.