Synthesis of 2-Formylpyrroles from Pyridinium Iodide Salts

The first I₂-mediated synthesis of 2-formylpyrroles from pyridinium salts is reported. This protocol enables the synthesis of diversely substituted 2-formylpyrroles in good yields under operationally simple conditions. The detailed mechanistic studies reveal that the reaction proceeds via a novel H₂O-triggered ring opening of the pyridinium salt and a subsequent intramolecularly nucleophilic addition sequence.