THE SYNTHESIS AND REACTIONS OF DIVINYL CARBONIUM IONS

A number of alkyl-substituted trienes have been protonated. In some cases, the existence of divinyl carbonium ions can be shown, while in others, a cyclization reaction leading to, cyclopentenyl carbonium ions takes place so rapidly that the presumed initially formed divinyl carbonium is never observed. Steric arguments are invoked to explain these differences. Complete n.m.r. and ultraviolet spectral data are presented in support of the assigned carbonium-ion structures. Some evidence has been obtained regarding the mechanism of the cyclization reaction. Finally, one of the cyclic carbonium ions is decomposed and the cyclic dienes which are produced are isolated and characterized.