Carbene−Alkene Complexes between a Nucleophilic Carbene and Electron-Poor Alkenes

Spirooxadiazoline 5 is a clean thermal source of tricyclo[6.2.1.0^2,7]undec-9-en-11-ylidene (7), a typical foiled carbene. Species 7 can be trapped efficiently at 165 °C by electron-deficient alkenes like acrylonitrile and fumaronitrile whereby the anti addition products are obtained exclusively. Higher temperatures, however, favor intramolecular reactions. Density functional theory (DFT) calculations predict the formation of a strong complex between both reactants which actually is a minimum on the free energy scale. These results confirm the nucleophilic character of foiled carbenes and the presence of a significant barrier toward rearrangement.