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)(η2-pyr) and TpW(NO)(PMe3)(η2-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(NH3)5(η2-pyrrole)]2+ an organic cycloadduct was successfully prepared with dimethyl fumarate, and this complex
was elaborated into advanced synthons to several naturally occurring pyrrolizidines.