Ramberg-Backlund rearrangement reaction conditions

One of the most important reactions of sulfones in general is the Ramberg-Backlund rearrangement, which involves the conversion of a-halosulfones to olefins with accompanying loss of hydrogen halide and sulfur dioxide under basic conditions (equation 48) ... 

The 1,5-thiazocine 566 was oxidized to chlorosulfone 457 by treatment with A -chlorosuccinimide in CCI4 and ot-MCPBA. The Ramberg-Backlund rearrangement involved conversion of the a-chlorosulfone 567 into the azepine 569 under basic conditions through the formation of episulfone 568 followed by extrusion of S02. The reaction was conducted using different bases, such as KO/-Bu (66% yield), aqueous KOH (43% yield), and alumina-supported KOH (63% yield) (Scheme 113) <2000JOC8367>. 

Thiirane A-oxides are effective precursors for sulfur monoxide (SO) under thermal conditions <1997JOC8366>. The sulfur monoxide has been trapped by a variety of dienes to form cyclic sulfoxides. Extmsion of SO2 from thiirane A,A-dioxides to form alkenes under thermal conditions is well known. The reaction takes place readily at room temperature in the presence of KO/-Bu in tetrahydrofuran (THF). It constitutes the final step of the Ramberg-Backlund rearrangement <20030R357, 1999CC217>. 

Contrary to what is observed in the Favorskii rearrangement, such a substitution product is seldom observed in the Ramberg-Backlund reaction, as cyclic a-halogenated sulfones generally give only the ring-contracted alkene under basic conditions. The sulfone which has a skeleton similar to the diene 37... 

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