Stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with carbon nucleophiles

The stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with allyltributylstannane and with ketene silyl acetals in the presence of a Lewis acid are described. Both the reactions occurred regioselectively at the allylic position via an SN2 process giving rise to a single product, respectively. Treatment of the products by the latter reaction with p-TsOH afforded various 3,4-anti- and 3,4-syn-disubstituted γ-lactones in a highly stereoselective manner and high yields.