Pyrrole studies. Part XV. Vilsmeier–Haack formylation of 1-substituted pyrroles

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Abstract
The ratio of α- to β-formylated products obtained by the Vilsmeier–Haack reactions with 1-alkyl- and 1-aryl-pyrroles is controlled mainly by steric factors. Electronic effects of 1-(p-substituted aryl) substituents upon the position of formylation of the pyrrole ring are small and are essentially inductive.