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

Abstract

A convenient diastereoselective synthesis of D-erythro- and L-threo-sphingosine derivatives is described. L-Serine-derived aldehyde (Garner's aldehyde) (2) was treated with 1-alkenyl-zirconocene chlorides (3) 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 2 with 1-alkenyl-ethyl-zinc, prepared from 3 and Et2Zn, in CH2Cl2 gave the unnatural threo-(syn-) isomers predominantly (anti/syn=1:12-15). © 2002 Elsevier Science Ltd. All rights reserved.