Sulfones, halo elimination with base

The reaction of an a-halo sulfone with a base to give an alkene is called the Ramberg-Bdcklund reaction. The reaction is quite general for a-halo sulfones with an (x hydrogen, despite the unreactive nature of a-halo sulfones in normal 8 2 reactions (p. 437). Halogen reactivity is in the order I>Br>Cl. Phase-transfer catalysis has been used. In general, mixtures of cis and trans isomers are obtained, but usually the less stable cis isomer predominates. The mechanism involves formation of an episulfone, and then elimination of SO9. There is much evidence for... 

S02. There is much evidence for this mechanism,311 including the isolation of the episulfone intermediate,312 and the preparation of episulfones in other ways and the demonstration that they give olefins under the reaction conditions faster than the corresponding a-halo sulfones.313 Episulfones synthesized in other ways (e.g., 6-62) are reasonably stable compounds but eliminate S02 to give olefins when heated or treated with base. 

The Ramberg-Backlund reaction converts a-halo sulfones into alkenes in the presence of a base with extrusion of S02. The a-metallated intermediates formed by the action of a polar base undergo 1,3-elimination with formation of unstable thiirane dioxides of type 83 that decompose into alkenes - - SO2 (cheletropic elimination). Halogenation is done under basic conditions using CBr2F2. The reactions has been applied to the synthesis of C-glycosides of type 84, as illustrated in Scheme 22.23. " ... 

---