Nucleophilic Carbenes of Pyrazoles Starting from Pseudo-Cross-Conjugated Mesomeric Betaines

Abstract

Pyrazolium-3-carboxylates, which belong to the class of pseudo-cross-conjugated heterocyclic mesomeric betaines, decarboxylate to give nucleophilic carbenes, which can be trapped as pyrazolium salts. An aldol addition, a Knoevenagel reaction, and a Cannizzaro-type reaction are presented, which are initiated by the strong basicity of the in situ generated pyrazol-3-ylidene. Keywords: decarboxylation, 1,2-ylide, pyrazol-3-ylidenes, pyrazolium-3-carboxylates