Mild Cu-catalyzed oxidation of benzylic boronic esters to ketones

The oxidation of benzylic boronic esters directly to the ketone is reported. This mild Cu-catalyzed method uses an ambient atmosphere of air as the terminal oxidant and is notably chemoselective. Oxidation of the C-B bond occurs selectively, even in the presence of unprotected alcohols. Initial investigation suggests the reaction proceeds through an alkylboron to Cu transmetallation, peroxide formation, and rearrangement to give the carbonyl.