Thermal and catalytic transylidations between halonium ylides and synthesis and reaction of stable aliphatic chloronium ylides

Intermolecular transylidation between halonium ylides under thermal and catalytic (rhodium(II) acetate) conditions, which makes it possible to synthesize a hitherto unknown kind of aliphatic chloronium ylides as well as a variety of bromonium and iodonium ylides, was developed. The uncatalyzed thermal transylidations of bromonium to iodonium ylides probably involve generation of a reactive carbene :C(SO₂CF₃)₂, being electrophilic in nature. Compared to the bromonium and iodonium ylides, the chloronium ylide serves as a much better progenitor for generation of carbenes (or carbenoids) and efficiently undergoes cyclopropanation of olefins such as cyclooctadiene under uncatalyzed thermal conditions. A greater leaving group ability of the λ³-chloranyl and λ³-bromanyl groups compared to that of the λ³-iodanyl group seems to be responsible for the observed differences in reactivity between these halonium ylides.