Diastereoselective synthesis of (2S,5S)- and (2S,5R)-N-benzyloxycarbonyl-5-hydroxypipecolic acids from trans-4-hydroxy-L-proline

An efficient diastereo selective synthesis of cis- and trans-5-hydroxy-(2S)-N-benzyloxycarbonyl pipecolic acids, starting from trans-4-hydrOXY-L-proline is described. The key synthetic strategies involve the regioisomeric ring expansion of keto ester 8 and diastereoselective reduction of ketone 11 in high selectivity and yield. (c) 2006 Elsevier Ltd. All rights reserved.