Alkene Difunctionalization Via b-Haloalkoxysulfonium Ions

Alkene difunctionalization via three-membered ring halonium ion intermediates is an important transformation in organic synthesis. The most straightforward method to generate the halonium intermediates is to use halogen cations, which are usually too unstable to accumulate in solution.

 Recently, we reported that halogen cations stabilized by dimethyl sulfoxide (DMSO) were successfully generated and accumulated in solution by low-temperature electrochemical oxidation. Reactions of DMSO-stabilized halogen cations such as Br⁺ and I⁺ with alkenes gave b-haloalkoxysulfonium ions. Subsequent treatment of the b-haloalkoxysulfonium ions with triethylamine gave α-halocarbonyl compounds via Swern−Moffatt type oxidation. Here, we report that treatment of the b-haloalkoxysulfonium ions with different bases gives different products, i.e. the use of sodium hydroxide and sodium methoxide gives halohydrins and epoxides, respectively.