Favorskii rearrangement

The Favorskii rearrangement (not to be confused with the Favorskii reaction), named for the Russian chemist Alexei Yevgrafovich Favorskii, is most principally a rearrangement of cyclopropanones and α-halo ketones which leads to carboxylic acid derivatives. In the case of cyclic α-halo ketones, the Favorski rearrangement constitutes a ring contraction. This rearrangement takes place in the presence of a base, sometimes hydroxide, to yield a carboxylic acid but most of the time either an alkoxide base or an amine to yield an ester or an amide, respectively. α,α’-Dihaloketones eliminate HX under the reaction conditions to give α,β-unsaturated carbonyl compounds.

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In the case of cylic α-halo ketones, the rearrangement occurs as depicted below:

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.

See also

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

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)