Stereoselective nitrenium ion cyclizations: asymmetric synthesis of the (+)-Kishi lactam and an intermediate for the preparation of fasicularin

The asymmetric synthesis of the (+)-Kishi lactam and an intermediate for the preparation of the marine natural product fasicularin is reported. The keystone of this divergent synthesis is the diastereoselective azaspirocyclization of an N-methoxy-gamma-arylbutanoamide, which is believed to proceed through the intermediacy of an N-acylnitrenium ion. (C) 2004 Elsevier Ltd. All rights reserved.