Activation of the C–OBpin Bond by Chromium Enables Catalytic Deoxyborylation of Benzylic Alcohols, Aldehydes, and Ketones

The reactivity of low-valent chromium in activating benzylic C–OB bonds is disclosed, which enables a chromium-catalyzed direct deoxyborylation protocol for benzylic alcohols without the need for substrate preactivation or addition of any activating reagents, providing a facile and step-effective synthesis of valuable benzylic boronate esters. Mechanistic studies reveal that a reactive low-valent chromium species mediates the cleavage of the sp3 C–OBpin bonds of benzyl borates formed in situ from benzylic alcohols and HBpin to generate the benzylchromium species that reacts with HBpin to afford the desired borylated products. The approach can also be applied to direct deoxyborylation of aromatic aldehydes and ketones.