<p>We thoroughly investigated mechanistic features of dichlorination of diazoacetates using PhICl<small><sub>2</sub></small> catalysed by pyridine. We found that the pyridine serves as a catalyst for decomposition of PhICl<small><sub>2</sub></small> to PhI and Cl<small><sub>2</sub></small>, leading to the dichlorination step being driven by the <em>in situ</em> generated Cl<small><sub>2</sub></small>. This type of activation was found to be applicable to other amine-catalysed chlorination reactions using PhICl<small><sub>2</sub></small>.</p>