Vilsmeier-Haak formylation of 3,5-dimethylpyrazoles

Abstract

Formylation of N-alkyl-3,5-dimethyl-1H-pyrazoles according to Vilsmeier-Haak led to the formation of the corresponding 4-formyl derivatives. 3,5-Dimethyl-1H-pyrazole having no substituent on the nitrogen atom failed to undergo formylation at the 4 position under analogous conditions. 3,5-Dimethyl-1H-pyrazole-4-carbaldehyde was synthesized by alkaline hydrolysis of methyl β-(4-formyl-3,5-dimethyl-1H-pyrazol-1-yl)propionate and subsequent heating of the acid thus formed. © 2006 Pleiades Publishing, Inc.