Acylpyrazolones possessing a heterocyclic moiety in the acyl fragment: intramolecular vs. intermolecular zwitterionic structures

Abstract

A series of acylpyrazolones possessing a methylene bridged heterocyclic unit in the acyl fragment are synthesized and characterized in solution and the solid state. It is found that the products exist in the solid state as intramolecular or intermolecular zwitterions between the tautomeric pyrazolone hydroxyl group and the nitrogen atom of the acyl substituents. Aliphatic amine units with a variable number and type of heteroatoms and ring size are attached and the type of zwitterions formed are analysed by single crystal XRD. It is observed that the products coordinate spontaneously with cesium carbonate being used as a base. These complexes are also studied by XRD.