Catalytic [3 + 2] Cycloaddition through Ring Cleavage of Simple Cyclopropanes with Isocyanates.

The catalytic synthesis of γ-butyrolactams was established via [3 + 2]-cycloaddition of cyclopropanes with isocyanates. An organotin iodide ate complex, MgBr(+)[Bu2SnBrI2](-), was employed as an effective catalyst. Simple cyclopropanes that lack aryl or vinyl substituents were useful precursors. Even acyl cyclopropanes were applicable. The hybrid characteristics of a tin complex, acidic MgBr(+) with nucleophilic tin iodide, was responsible for the catalytic reaction.