Alkadienyl and Polyenylic Cations

Richey and their co-workers24 have observed a substantial number of alkadienyl cations. Sorensen79 has observed divinyl and trivinyl cations 27 and 28. 

Alkadienyl cations show great tendency to cyclize and these reactions have been followed by NMR80. More recently several novel fulvenes have been protonated to 

Alkadienyl cations such as the 1,3,5-trimethylheptadienyl cation 85 show great tendency to cyclize [Eq. (3.37)] and these reactions have been followed by NMR.240 Several novel fulvenes have been protonated to their corresponding dienyl cations241 (e.g., 86 and 87). 

Sorensen and co-workers242 have studied the stereochemistry of ring closure of arylallyl cations to bicyclic trienyl cations. Similar studies on 1-phenylallyl cations have been carried out by Olah et al.225 Persistent polyenylic cations generated upon incorporation of cinnamyl alcohols in zeolitic matrix have been identified on the basis of IR and UV-visible spectroscopy 243 

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