Asymmetric [2,3]-Wittig Rearrangement via Chirality Transfer

Significance

A base-induced epoxide ring opening of the epoxy-allyl ether, followed by Brook rearrangement, generated the carbanion, which underwent an enantioselective [2,3]-Wittig rearrangement via chirality transfer from the epoxide. The enantioselectivity was very dependent upon the solvent; the highest enantioselectivities were obtained using diethyl ether and 1,4-dioxane, while THF failed to promote enantioselectivity. It is quite remarkable that a carbanion conjugated to both a double bond and a naphthyl group can retain its configuration. It has not yet been proven whether the carbanion is actually generated prior to the [2,3]-Wittig rearrangement or whether the mechanism proceeds through an intermediate of the Brook rearrangement without involvement of a carbanion.