Ramberg-Bäcklund rearrangement

What is Ramberg-Bäcklund rearrangement?

The Ramberg-Bäcklund rearrangement is a well-known transformation of α-halosulfones into olefins, which was first discovered by Ramberg and Bäcklund in 1940. This reaction is sometimes referred to as the Ramberg-Bäcklund reaction, Ramberg-Bäcklund elimination, Ramberg-Bäcklund olefination, Ramberg-Bäcklund synthesis, or Ramberg-Bäcklund olefin synthesis.

Ramberg-Bäcklund rearrangement - general reaction scheme - Ramberg-Bäcklund reaction - Ramberg-Bäcklund elimination - Ramberg-Bäcklund olefination - Ramberg-Bäcklund synthesis - Ramberg-Bäcklund olefin synthesis
Ramberg-Bäcklund rearrangement

It is a base-promoted reaction that occurs at mild conditions and involves the extrusion of SO2 via an episulfone intermediate. The reaction is applicable to almost all α-halosulfones that have at least one α-hydrogen. The mechanism of the reaction involves the deprotonation of α-hydrogen to generate a sulfonyl carbanion, which then undergoes an intramolecular nucleophilic displacement of α-halogen to form an episulfone intermediate. This intermediate is subsequently converted to the corresponding olefin.

The Ramberg-Bäcklund rearrangement usually gives the cis-elimination product and occurs at moderate temperatures, requiring only a dilute base. It is noteworthy that α-halosulfones are prone to 1,3-elimination to form episulfone when exposed to a base, regardless of the number of α-halogens. Furthermore, the base treatment of trichloromethyl sulfones leads to the formation of sulfonic acid.

The application of the Ramberg-Bäcklund rearrangement in organic synthesis is extensive, particularly for the synthesis of natural products and C-glycosides.

References

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