Osmium(II)-, Rhenium(I)-, and Tungsten(0)-Promoted Dipolar Cycloaddition Reactions with Pyrroles: Exploiting the Azomethine Ylide Character of This Heterocycle

Complexes of the form TpRe(CO)(MeIm)(η 2 -pyr) and TpW(NO)(PMe 3 )(η 2 -pyr) (where pyr = 1-methylpyrrole, 2-methylpyrrole, and 2,5-dimethylpyrrole) were prepared and combined with a range of potential dipolarophiles. In several cases a dipolar cycloaddition resulted in the formation of 7-azanorbornene complexes (one crystal structure for each metal is presented), but attempts to develop a general route to the organic bicyclic system were unsuccessful. Using the complex [Os(NH 3 ) 5 (η 2 -pyrrole)] 2+ an organic cycloadduct was successfully prepared with dimethyl fumarate, and this complex was elaborated into advanced synthons to several naturally occurring pyrrolizidines.