1,3-DIPOLAR CYCLOADDITIONS OF PHOTOINDUCED CARBONYL YLIDES - PART 2 -PHOTOREACTIONS OF ALPHA,BETA-UNSATURATED GAMMA,DELTA-EPOXY DINITRILESAND ETHYL VINYL ETHER

Photoinduced carbonyl ylides B, C, E and F from the alpha,beta-unsatur ated gamma,delta-epoxy dinitriles 2, 3, 5 and 6, respectively, undergo 1,3-dipolar cydoaddition with ethyl vinyl ether, leading to the tetra hydrofuran system, The cydoaddition proceeds with high regioselectivit y affording predominantly the exo-adduct, However, the ylide from the mononitrile 1 and dinitrile 4 gives little or no adduct, The observed regioselectivity and the difference of the reactivity in these cycload ditions can be nicely accommodated in terms of semiempirical AM1 calcu lations, The reactivity of the cycloaddition depends on the LUMO energ y level and the C(gamma),C(delta) distance of the ylide.