Twenty-two dichlorinated methylketones have been submitted to Favorskii rearrangement in NaOMe MeOH. Distribution of products is strongly dependent on substitution. Primary dichloromethyl-ketones (R2= H) gave rise to Favorskii esters only. Results are explained by a cyclopropanone intermediate, which is formed stereospecifically by disrotative closure of a delocalized zwitter-ion. Opening of the cyclopropanone intermediate is affected by steric ...
