The mechanism of the Vilsmeier–Haack reaction. Part III. Structural and solvent effects

Abstract

New kinetic data on the Vilsmeier–Haack reaction of heterocyclic compounds are reported which permit the conclusions that (i) the reaction is very selective, as shown by a ρ value of –7·3 for the formylation of thiophen derivatives in chloroform, (ii) the rate of substitution is only affected to a small extent by the polarity of the solvent, and (iii) the rate of substitution is highly dependent on the nature of amide. The reaction with NN-dimethylacetamide–carbonyl chloride complex proceeds ca. 5 × 10³ times slower than the reaction with corresponding NN-dimethylformamide complex.