The α-dichlorination of aldehydes needs two successive enolization steps and for a successful transformation the reaction has to be performed under acid-catalysis. In fact, in an alkaline medium, the halogenation would result in oxidation and aldol condensation. [16b] After the introduction of the first Cl-function, acid-catalysis, owing to the strongly reduced basicity of the carbonyl group, is unable to promote a sufficiently rapid second chlorination step and, as a ...
