Homo-Favorskii rearrangement

The homo Favorskii rearrangement is the rearrangement of β-halo ketones and cyclobutanones, which in ring systems may yield ring contraction. This rearrangement takes place in the presence of a base, yielding a carboxylic acid derivative corresponding to the nucleophile (most often the base itself). E1cb will occur if α-carbon adjacent to the halogen atom has hydrogens on it.