4-substituted Ramberg-Backlund rearrangement

A novel tandem process has been reported " for the preparation of allylic amines, ethers, and sulfides from a-bromo-a, jS-unsaturated sulfones. The process is believed to proceed via an initial conjugate addition followed by proton exchange and Ramberg-Backlund rearrangement (see Scheme 75). A new variant of the Ramberg-Backlund reaction has been described in which a, /f-epoxy sulfones (319), on treatment with base, are converted into a range of mono-, di-, and tri-substituted allylic alcohols (320). 

Q -monoamon is more reactive and more basic 12.5). When fully substituted at a the deprotonation of phenylsulfonyl methyl sulfones at a also initiates the Ramberg-Backlund rearrangement with loss of phenylsulfinate ion. When no a -CH is available for deprotonation, treatment with base serves to eliminate triflinate, as in eq 6, and is also used to create cyclic vinyl sulfones when the a-dialkylation is done with a,ffii-dihalides. ... 

Such reductive ring contractions of sulfones are formally similar to two other methods capable of supplanting a sulfur atom by a carbon-carbon double bond the Ramberg-Backlund and Stevens rearrangements. The distinguishing feature of this novel approach to pyolobutenes consists in the resultant higher level of alkyl substitution at the sp -hybridized centers. 

Formation of an a-metalated sulfone in which the a position is substituted with a halide promotes alkene formation in what is known as the Ramberg-Backlund reaction (or rearrangement). Intramolecular displacement of the halide gives an... 

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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