In the presence of a catalytic amount of chiral phosphoric acid, nucleophilic addition of N-monosubstituted hydrazones to N-Boc imines affords differentially protected vicinal diamines in the form of b-amino N,N’-dialkyldiazenes in excellent yields with high chemo-, diastereo-, and enantioselectivity. This catalytic asymmetric aza-Mannich reaction represents the first example in which N-alkyl hydrazones serve as a-azo carbanion equivalents to provide vicinal diamines with control of the two contiguous stereocenters. The adducts are readily converted into the monoprotected or free diamines and derivatives thereof