Stepwise insertion of carbenes into C–H bonds: the case of foiled carbenes

The reactivity of stabilized-nucleophilic carbene tricyclo[6.2.1.02,7]undec-9-en-11-ylidene (9) toward C–H insertions has been investigated. It is shown that 9 can only insert into acidic C–H bonds, for example, in malononitrile. In this case, evidence for a stepwise process has been obtained. Protonation of the carbene leads to an ion pair composed of a carbocation and a carbanion, which subsequently reacts and gives rise to the formal insertion product anti 10.