Rate measurements of certain Vilsmeier–Haack reactions. Part 2. The effect of N-substituents in the amide

Abstract

Rate measurements on the reaction between a series of amide–POCl₃ complexes (2a–h) and ethyl 2,4-dimethylpyrrole-3-carboxylate in 1,2-dichloroethane were used to study the effect of N-substituents in amides (1a–h) on the Vilsmeier–Haack reaction. The results obtained are generally consistent with the expected steric and l strain effects with the exception of the morpholide and the two N-substituted piperazides which showed unexpected reactivity; a reason for this exceptional reactivity is suggested. The morpholide is recommended for the benzoylation of pyrroles.