Diastereoselective Addition of Racemic α-Boryl Organozinc Reagents to Aldimines.

The addition of alkylzinc reagents to imines is a key route to amines, but suffers from poor selectivity when racemic secondary alkylzincs are employed. Herein, we report a transition-metal-free diastereoselective addition of racemic α-boryl organozincs to aldimines, affording anti-β-aminoborons with good to excellent diastereoselectivities. Furthermore, Cu-catalyzed addition of racemic α-boryl organozincs to N-tert-butanesulfinyl aldimines afforded enantioenriched anti-β-aminoborons, preferentially delivering one of the four possible stereoisomers with high selectivity.