Copper-Catalyzed Asymmetric Synthesis of α-Amino Boronate Esters

Significance

The asymmetric addition of (bispinacol)boron to various N-tert-butanesulfonyl ald­imines produces useful α-amino boronate esters in good yields and excellent diastereoselectivities. The reaction is not sensitive to steric or electronic changes on the aryl groups. The high synthetic utility of the products is demonstrated by the synthesis of the proteasome inhibitor bortezomib in five steps.