Access to Enantioenriched 1,<i>n</i> ‐Diols by Cu‐Catalyzed Enantioselective Protoboration and Hydroboration of Alkenyl Ethers

We report two catalytic enantioselective borylation/oxidation sequences that streamline access to either enantioenriched 1,2‐ or 1,3‐diols starting from <i>O</i> ‐benzyl‐protected allylic alcohols as a single precursor. The approach takes advantage of the complementary regioselectivity of the Cu‐catalyzed protoboration and the Cu‐catalyzed hydroboration of disubstituted alkenes, which effectively install a borane function and a hydrogen atom on opposite C(sp ² ) carbon atoms of a carbon–carbon double bond. The two methods feature broad substrate scope and are amenable to large scale without measurable loss of the catalytic efficiency. Both protocols display high levels of regioselectivity and enantioselectivity.