Diastereoselective imino-pinacol coupling of chiral imines promoted by Mg(0) and a Grignard reagent

The reaction of chiral imines, derived from aromatic aldehydes and (S)-valinol, with a Grignard reagent in the presence of Mg(0) afforded imino-pinacol coupling products instead of alkylated amines, with a high level of diastereoselectivity. The chiral auxiliary in the product was successfully removed via dehydration followed by hydrolysis, and the corresponding (R,R)-ethylenediamine derivative was obtained as the N-Boc protected form.