Efficient stereodivergent synthesis of erythro- and threo-sphingosines: unprecedented reversal of the stereochemistry in the addition

A convenient diastereoselective synthesis of d-erythro- and l-threo-sphingosine derivatives is described. l-Serine-derived aldehyde (Garnerʹs aldehyde) () was treated with 1-alkenyl-zirconocene chlorides () in the presence of ZnBr2 in THF to give the natural erythro-(anti-) isomers with high diastereoselectivity (anti/syn=12–20:1). In contrast, reaction of with 1-alkenyl-ethyl-zinc, prepared from and Et2Zn, in CH2Cl2 gave the unnatural threo-(syn-) isomers predominantly (anti/syn=1:12–15).