Generation of Delocalized Carbocations

Ketenes are useful sources of carbenes in the gas phase but are rarely applied in solution, owing to their tendency to dimerize and to accept nucleophiles. However, the sterically encumbered ketene 36, derived from cyclogeranium 

Bicycloalkylidenes. a-Delocalization in bicyclic carbocations provides the opportunity to detect the protonation of bicycloalkylidenes. An obvious choice was the 2-norbomyl cation (66), for which symmetrical bridging (equivalence 

62 in the presence of alcohols afforded mixtures of norbomene (67), nortricy- 

Bicyclo[2.1.1]hex-2-ylidene (78) is expected to be longer lived than 2-norbomylidene (65), owing to the enhanced ring strain of the intramolecular products. Although vacuum thermolysis of the tosylhydrazone salt 74 gives bicyclo[2.1.1]hex-2-ene,38 intermolecular reactions of 78 prevail in solution.36 

Bicycloalkenylidenes. The vacant p orbitals of 5-norbomen-2-ylidene (91) and of 2-norbomen-7-ylidene (100) interact with the 7t bonds, thus enhancing the nucleophilicity of the divalent carbon.40 Protonation of these carbenes leads 

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