Asymmetric synthesis of hydroxylated pyrrolizidine, indolizidine, and (+)-alpha-conhydrine via ruthenium-catalyzed hydrogenation.

The enantioselective ruthenium promoted hydrogenation of beta-keto ester, derived from (S)- or (R)-proline and (S)-pipecolic acid, provided a new efficient route to hydroxylated pyrrolizidine or indolizidine ring systems in diastereomeric excesses up to 99%. A practical synthesis of (+)-alpha-conhydrine is also reported. Copyright 2000 Wiley-Liss, Inc.