Reaction of phosphorus pentachloride with N-vinylimidazole and N-vinylbenzimidazole

Abstract

Earlier, we have found that N-vinylpyrazoles are phosphorylated with phosphorus pentachloride at the double bond to give rise to unsaturated organophosphorus compounds [1]. N-Vinylimidazoles contain-ing in the ring highly basic separated nitrogen atoms of the pyridine type react with phosphorus pentachloride in a different manner. In these reactions, the first and foremost are the donor–acceptor interactions. N-Vinylimidazole I reacts with phosphorus pentachloride (even in the excess of the latter) to give the donor– acceptor complex III with participation of the pyridinium nitrogen atom. As a result, the electron–acceptor properties of the ring increase and the nucleophilicity of the N-vinyl group decreases hampering its phosphorylation. The treatment of azole I with the solution of phosphorus pentachloride in benzene saturated with hydrogen chloride affords complex compound IV containing the protonated nitrogen atom in the 3 position.