Stereoselective synthesis of optically active cyclopenta[c]pyridines and tetrahydropyridines

The intramolecular Pauson-Khand and ring closing metathesis (RCM) reactions of nitrogen containing chiral enynes and dienes are described. The enyne and diene systems comprised of N-propargylated and N-allylated units are constructed on chiral homoallylic or homopropargylic alcohol backbones, respectively, via S(N)2 and/or modified Mitsunobu reactions. The racemic homoallylic and homopropargylic alcohol derivatives were successfully resolved in high ee (93-99%) by applying chemoenzymatic methods using various lipases such as PS-C II, Lipozyme, and CAL-B. Each enantiomerically enriched enyne afforded the most conformationally stable diastereomeric cyclopenta[c]pyridine ring system as the sole product, whereas enantiomerically enriched dienes gave tetrahydropyridine derivatives as a result of intramolecular Pauson-Khand and RCM reactions, respectively. (C) 2012 Elsevier Ltd. All rights reserved.