Tuning the Chemoselectivity of the Metathesis Reactions of N‐Substituted 2‐Azabicyclo[2.2.1]hept‐5‐en‐3‐one

Abstract By using the second‐generation Hoveyda–Grubbs precatalyst, the metathesis transformations of N ‐substituted 2‐azabicyclo[2.2.1]hept‐5‐en‐3‐one derivatives have been explored. In the absence of any external alkene (cross‐metathesis partner), substituted pyrrolizidin‐3‐one derivatives were obtained by ring‐opening metathesis/ring‐closing metathesis tandem reactions. In the presence of an external alkene, N ‐substituted 2‐pyrrolidinones were isolated by ring‐opening metathesis/cross metathesis tandem reactions. In this case, and by using an alkene other than ethylene (allyltrimethylsilane), the reaction was totally chemo‐ and diastereoselective. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)