An approach to functionalized cubanes. Regioselectivities and frontier molecular orbital analysis in the addition of dimethyl cyclobutadiene-1,2-dicarboxylate to quinones

Abstract

4 + 2 Cycloaddition between dimethyl cyclobutadiene-1,2-dicarboxylate and benzoquinone, 4, gives 6, 7 and 8 in the ratio 15:4:1. Similarly naphthoquinone, 5, furnishes 9, 10 and 11 in the ratio 11:1:2. Formation of symmetrical adducts is predominent in both cases, Irradiation of major adducts 6 and 9 results in a cascade of photorearrangements. Semiempirical AM1 calculations are used to rationalize the regioselectivities.