O-Methylation of a sulfone with methyl fluoride – antimony pentafluoride – sulfur dioxide. Preparation and properties of tetrahydro-1-methoxythiophenium 1-oxide hexafluoroantimonate

Abstract

Reaction of sulfolane (tetrahydrothiophene 1,1-dioxide) (1) with methyl fluoride – antimony pentafluoride in liquid sulfur dioxide gives crystalline tetrahydro-1-methoxythiophenium 1-oxide hexafluoroantimonate (2), thereby providing the first characterized example of an alkoxysulfoxonium salt. This salt (2) is also formed, but more slowly, by reaction of methyl fluoride with the crystalline 1:1 complex of sulfolane and antimony pentafluoride. Reaction of 2 with nucleophiles leads to transfer of the methyl group, a facile process even with such weak nucleophiles as nitrobenzene and phenyl N,N-dimethylsulfamate. Spectroscopic evidence has been obtained for O-methylation of other sulfones, either by reaction with MeF•SbF5•SO2, or via the sulfone•SbF5 complex and methyl fluoride, or by transmethylation with 2.