Rh₂(II)-Catalyzed Ring Expansion of Cyclobutanol-Substituted Aryl Azides To Access Medium-Sized <i>N</i>‑Heterocycles

A new reactivity pattern of Rh2(II)-N-arylnitrenes was discovered that facilitates the synthesis of medium-sized N-heterocycles from ortho-cyclobutanol-substituted aryl azides. The key ring-expansion step of the catalytic cycle is both chemo­selective and stereo­specific. Our mechanistic experiments implicate the formation of a rhodium N-arylnitrene catalytic intermediate and reveal that sp3 C–H bond amination of this electrophilic species is competitive with the ring-expansion process.