Chemo- and Regioselective Reduction of Epoxides with Sodium Borohydride in Mixed Solvent Containing Methanol

Mono- and gem-disubstituted epoxides were reduced to more substituted alcohols in good to high yields (73–100%) and in high regioselectivities (89–100:11–0) by sodium borohydride in a mixed solvent of t-butyl alcohol–methanol or 1,2-dimethoxyethane-methanol. The reaction of disubstituted epoxide depends on the steric hindrance and the position of the substituents. Trisubstituted epoxides were not reduced by the present reducing system. The reactivity order of epoxides by the present reducing system was mono->2,2-di->2,3-di->>trisubstituted epoxides. The chemoselectivity of the present reducing system is excellent. Thus, epoxides were selectively reduced in the presence of such reducible groups as carbamoyl, carboxyl, nitro, cyano, and bromo.