Markovnikov Alcohols via Epoxide Hydroboration by Molecular Rock-Forming Metal Catalysts

Synthesis of branched “Markovnikov” alcohols is crucial to various chemical industries. The catalytic reduction of substituted epoxides under mild conditions is a highly attractive method for preparing such alcohols. Classical methods based on heterogeneous or homogeneous transition metal-catalyzed hydrogenation, hydroboration or hydrosilylation usually suffer from poor selectivity, reverse regioselectivity, limited functional group compatibility, high cost and/or low availability of the catalysts. Here we report the discovery of a highly regioselective (up to 99%) hydroboration of nonsymmetrical epoxides catalyzed by ligated alkali metal triethylborohydride, an old archetypal reductant in organic chemistry. The chemoselectivity and turnover efficiencies of the present catalytic approach are excellent. Thus, terminal and internal epoxides with ene, yne, aryl, and halo groups were selectively and quantitatively reduced under a substrate-to-catalyst ratio (S/C) of up to 1000.