Concomitant Nitrene and Carbene Insertion Accompanying Ring Expansion: Spectroscopic, X‑ray, and Computational Studies

Reinvestigation of the thermolysis
of azido-meta-hemipinate (I) yielded, in addition to
known II, unusual
products III and IV. These products are
formed via a rare intramolecular nitrene insertion into an adjacent
methoxy C–H bond followed by an intermolecular reaction during
a ring-expansion and a ring-extrusion reaction followed by a carbene
insertion. The structures of the new compounds were confirmed using
a battery of techniques, including HRMS (ESI-QTOF) and 2D NMR as well
as X-ray crystallography for compound IV. Density functional
theory methods were used to support the proposed mechanism of formation
of the products.