Highly syn-Selective Additions of Allylic Stannanes to Protected .alpha.-Amino Aldehydes

The γ-oxygenated allylic stannane (R)-(8b) adds to the threonine- and serine-derived N-BOC aldehydes (1) and (14) in the presence of MgBr 2 to afford the syn adducts 9b and 15b as the sole products