The asymmetric synthesis of all four stereoisomers of 4-hydroxypipecolic ac
id (1) from the polyfunctionalized chiral building blocks delta -amino beta
-keto esters (S-S,R)-(+)-5 or (R-S,S)-(-)-5 is described. Key steps in the
synthesis are the stereoselective reductions of b-phenylpiperidine-2,4-dio
ne (6) and N-sulfinyl delta -amino beta -keto esters 5 to cis 4-hydroxy 2-p
iperidinone 7 and syn-delta -amino beta -hydroxy ester 9, respectively. The
only protecting/deprotecting group chemistry required is related to the ox
idation step.