Intermolecular reactions of foiled carbenes with N-H bonds: evidence for an ylidic pathway.

The chemistry of endo-tricyclo[6.2.1.0 (2.7)]undec-9-en-11-ylidene (10), an archetypal foiled carbene, has been investigated. The intermolecular reactions of 10 are most conveniently performed with oxadiazoline 6 because the corresponding diazirine can be obtained only in very low yield. Furthermore, the aziridinyl imine is difficult to decompose and the tosylhydrazone sodium salt poorly soluble in common organic solvents. Photolysis of 6 in diethylamine leads merely to a reduction of the diazo group and regeneration of acetyl hydrazone 5, whereas thermolysis cleanly affords tertiary amine 12(anti) in 77% yield. Calculations show that even stabilized-nucleophilic carbenes react with amines through an ylidic pathway and not by a concerted insertion into the N-H bond. Nevertheless, in the gas phase, norbornen-7-ylidene (13) is predicted to be stabilized by one molecule of NH3 more efficiently through a hydrogen bond than by ylide formation.