[New development of ammonium ylide chemistry].

Benzylammonium N-alkylides were generated by reaction of N-[1-(trimethylsilyl)alkyl]benzylammonium salts with cesium fluoride in DMF or HMPA, and their rearrangement products were investigated. [2,3]Sigmatropic rearrangement of the ylides initially occurred to give isotoluene derivatives and then they were transformed into Sommelet-Hauser rearrangement products and/or Stevens products. The isotoluenes having bicyclic structures were stable at room temperature and aromatized with the aid of a base. The relationship between the configuration of cyclic ammonium ylides and the rearrangement paths is described.