Favorskii rearrangement

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The Favorskii rearrangement is the transformation of haloketones to branched-chain or ring-contracted carboxylic acid derivatives in the presence of a base, typically alkoxide or an amine. α,α’-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.

[edit] Mechanism

The reaction mechanism is thought to involve the formation of an enolate on the side of the ketone away from the chlorine atom. This enolate cyclizes to a cyclopropanone intermediate which is then attacked by the hydroxide nucleophile.

Usage of alkoxide anions such as sodium methoxide, instead of sodium hydroxide, yields the ring-contracted ester product.

[edit] See also

• A classic cubane synthesis contains two Favorskii rearrangements.
• Wallach degradation

[edit] References

• Favorskii, A. E. J. Russ. Phys. Chem. Soc. 1894, 26, 590.
• Favorskii, A. E. J. Russ. Phys. Chem. Soc. 1905, 37, 643.
• Favorskii, A. E. J. Prakt. Chem. 1913, 88, 658.
• Kende, A. S. Org. React. 1960, 11, 261-316. (Review)
• Organic Syntheses, Coll. Vol. 4, p.594 (1963); Vol. 39, p.37 (1959). (Article)
• Organic Syntheses, Coll. Vol. 6, p.368 (1988); Vol. 56, p.107 (1977). (Article)
• Shioiri, T.; Kawai, N. J. Org. Chem. 1978, 43, 2936.
• Organic Syntheses, Coll. Vol. 7, p.135 (1990); Vol. 62, p.191 (1984). (Article)