Asymmetric Induction in Intramolecular [2 + 2]-Photocycloadditions of 1,3-Disubstituted Allenes with Enones and Enoates
Irradiation of optically active allenes (89-92% ee) appended to enones and enoates affords alkylidenecyclobutane photoadducts with high levels of asymmetric induction (83-100%) derived exclusively from the allene fragment. The substrates studied include allenes tethered to enones such as 1,3-cyclohexanedionea nd 1,3-cyclopentanedione, as well as allenes tethered to functionalized coumarins. The enantiomer ratios of the photoadducts were quantified by derivatization of the products as the corresponding Mosher MTPA esters and analysis by ^1H NMR spectroscopy. The exo-methylenecyclobutanes obtained upon irradiation of allene-mumarins are isolated as single olefin diastereomers. Irradiation of a coumarin tethered at C(5) with an optically active allene affords an alkynyl-substituted oxepane with complete asymmetric induction.
© 1994 American Chemical Society. Received January 3, 1994. C.A.H. thanks W. R. Grace and Co. for a summer fellowship award. M.S.S. is grateful to the Office of Naval Research for a graduate fellowship. We are grateful to Professor K. I. Hardcastle (California State University, Northridge) for obtaining an X-ray crystal structure of (±)-25. This research has been supported by a Beckman Young Investigator Award, the National Science Foundation (CHE-9221945), and a Camille and Henry Dreyfus New Faculty Award (NF-92-46).
Supplemental Material - ja00094a017_si_001.pdf
Supplemental Material - ja6622.pdf