Cu-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones to access benzylboronic esters

Organoboron compounds are widely used in synthetic chemistry, pharmaceutical chemistry and material chemistry. Among various organoboron compounds, benzylboronic esters are unique and highly reactive, making them suitable benzylation reagents. At present, the synthetic methods for the syntheses of benzylboronic esters are still insufficient to meet their demands. It is necessary to develop novel and practical methods for their preparation. In this work, a novel copper-catalyzed deoxygenative gem-hydroborylation of aromatic aldehydes and ketones has been developed. This direct and operationally simple protocol provides an effective approach for the synthesis of a variety of primary and secondary benzylboronates, in which broad functional group tolerance was presented. Widely available B2pin2 (pin = pinacol) was used as the boron source and alcoholic proton was applied as the hydride source.