Reaction of 1,3-dioxolans with iodine monochloride: the scope and mechanism of formation of 1,3-dioxolan-2-ylium dichloroiodates(I)

Abstract

Treatment of a series of 2-substituted-4,4,5,5-tetramethyl-1,3-dioxolans with iodine monochloride afforded the appropriate 2-substituted-4,4,5,5-tetramethyl-1,3-dioxolan-2-ylium dichloroiodate(I) salts in excellent yields. In contrast to the stable 2-aryl-substituted salts, the 2-alkyl and unsubtituted derivatives were relatively labile. While 2-phenyl-1,3-dioxolan and 2-phenyl-1,3-dioxan afforded low yields of unstable salts, crystalline products could not be isolated from 4,5-disubstituted dioxolans. The reaction was inhibited by electron-withdrawing 4- and 5-substituents. From a study of the effects of photolysis and added iodine, the mechanism is proposed to involve a hydride ion transfer. Possible reasons for the formation of dichloroiodate(I) rather than monohalide salts, are outlined. The stability of the 2-aryl-substituted salts is discussed in terms of charge distribution in the cation and possible aryl–anion interactions.