1,3-Dipolar cycloadditions of photoinduced carbonyl ylides. Part 2. 1 Photoreactions of α,β-unsaturated γ,δ-epoxy dinitriles and ethyl vinyl ether

Photoinduced carbonyl ylides B, C, E and F from the α,β-unsaturated γ,δ-epoxy dinitriles 2, 3, 5 and 6, respectively, undergo 1,3-dipolar cycloaddition with ethyl vinyl ether, leading to the tetrahydrofuran system. The cycloaddition proceeds with high regioselectivity 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 cycloadditions can be nicely accommodated in terms of semiempirical AM1 calculations. The reactivity of the cycloaddition depends on the LUMO energy level and the C(γ),C(δ) distance of the ylide.