Optimisation of enantioselectivity for the chiral base-mediated rearrangement of bis-protected meso-4,5-dihydroxycyclohexene oxides: asymmetric synthesis of 4-deoxyconduritols and conduritol F

A strategy based on diastereoselective epoxidation of a cyclohexene followed by chiral lithium amide-mediated epoxide rearrangement has been used to synthesise an allylic alcohol building block of >95% ee. The key step is the enantioselective rearrangement of a bis-protected meso-4,5-dihydroxycyclohexene oxide. A range of protecting groups and chiral base structures were surveyed in order to find the optimum protocol for high enantioselectivity. Using a tert-butyldimethylsilyloxy protecting group and a norephedrine-derived chiral base, a 93% yield of an allylic alcohol of >95% ee was achieved. To demonstrate the synthetic utility, this allylic alcohol was subsequently transformed into 4-deoxyconduritols and (+)-conduritol F.