N-Acyliminium Ion Chemistry: Improving the Access to Unsaturated -Lactams and Their N--Methoxylated Derivatives: Application to an Expeditive Synthesis of ()-Crispine A

An improved synthesis of unsaturated gamma-lactams by condensation of various primary amines with 2,5-dimethoxy-2,5-dihydrofuran is described. A modified mechanism for this reaction is suggested. Synthesis of theirN-alpha-methoxylated derivatives, asN-acyliminium ion precursors, is also reported. Finally, a short synthesis of (+/-)-crispine A is presented as an illustrative application.