A zincated N,N-dimethylhydrazone of a ketone undergoes stereospecific syn addition to E- or Z-alkenylboronate to generate a gamma-Zn/B dimetallic intermediate, which reacts with a carbon electrophile to give a gamma-borylhydrazone in good yield with excellent diastereoselectivity, creating two to four contiguous stereogenic centers in a one-pot reaction.