• substrate =  a'-enolizable a-halo-ketone

mechanism:

remarks:

• The reaction is both regio- and stereoselective.
• There are two major variations of the Favorskii rearrangement: the homo-Favorskii's when b-halo-ketones are treated with base in the presence of a nucleophile, going through the corresponding cyclobutanone, and the quasi-Favorskii's when the a-halo-ketone does not have any enolizable hydrogen.

example:

references:

Synth. Commun. 2006, 36, 259.
Eur. J. Org. Chem. 2005, 4687.
Curr. Org. Chem. 2005, 9, 1713.
Tetrahedron 1986, 42, 1621.
Tetrahedron Lett. 1981, 22, 1733.
J. Am. Chem. Soc. 1961, 83, 3980.
Organic Reactions 1960, 11, 261.