Asymmetric induction in intramolecular [2 + 2]-photocycloadditions of 1,3-disubstituted allenes with enones and enoates

Article abstract of DOI:10.1021/ja00094a017

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-cyclohexanedione and 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-coumarins 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.