1969 Articles

Favorskii rearrangement of some α-Bromo-ketones

Turro, Nicholas J.; Gagosian, Robert B.; Rappe, Christoffer; Knutsson, Leif

The base-induced rearrangement of α-halogenoketones to give carboxylic acid derivatives (Favorskii rearrangements) occurs by at least two mechanisms. The stereochemistry, and structure of many Favorskii products can be explained in terms of a cyclopropanone intermediate. However, a "benzylic-like" rearrangement appears to operate when the substrate ketone bears no α'-hydrogen, when the α'-hydrogen is relatively non-acidic, or when steric or strain factors inhibit cyclopropanone formation. In addition, the formation of a dipolar intermediate which may precede (or follow) cyclopropanone formation is supported by theoretical considerations, loss of stereospecificity upon rearrangement in polar solvents, the formation of α-substitution products as a side reaction, and the trapping of a possible Favorskii intermediate "dehydrohalogenate" to form a common intermediate leading to the same product.