Pyrroline and Cycloadduct Complexes

Liberation of the organic ligand in 3-pyrroline complexes can be accomplished in good yield either by oxidation (CeIV or DDQ), or by heating under anaerobic conditions.12,14 Synthesis of the pyrrolizinone 109 is accomplished by first reducing the ring-opened 2//-pyrrolium 

In contrast to the conventional Diels-Alder reaction with free pyrroles, which requires specialized functionalization on both the pyrrole and dienophile, the [2+3] dipolar cycloadditions described herein allow the use of simple alkenes (i.e., bearing at least one electron-withdrawing group) and pyrroles containing no electron-withdrawing groups. Use of 

Notes a Prepared from crude reaction mixtures. 

Diastereoselectivity based on h NMR data prior to chromatographic separation. 

---