Reactivity vs. Stability of Cyclopropenium Substituted Phosphonium Salts

International audienceThe stability vs. reactivity of electrophilic 3-(triphenylphosphonio)-cyclopropenium salts towards a neutral nucleophile, such as triphenylphosphane, is reported. Depending on the nature of cyclopropenyl substituents (R), the three-membered cyclic structure is preserved (R = Ph) or evolves by ring opening to the isomeric linear allene (R = Mes). The respective formation of 1,3-bis(triphenylphosphonio)-2,3-diphenylcyclopropene and 3,3-bis(triphenylphosphonio)-1,1-dimesitylallene products is rationalized on the basis of steric and electrostatic constraints