Synthesis and Structural Characterization of 1- and 2-Substituted Indazoles: Ester and Carboxylic Acid Derivatives

Abstract

A series of indazoles substituted at the N-1 and N-2 positions with estercontaining side chains -(CH 2 ) n CO 2 R of different lengths (n = 0-6, 9, 10) are described. Nucleophilic substitution reactions on halo esters (X(CH 2 ) n CO 2 R) by 1H-indazole in alkaline solution lead to mixtures of N-1 and N-2 isomers, in which the N-1 isomer predominates. Basic hydrolysis of the ester derivatives allowed the synthesis of the corresponding indazole carboxylic acids. All compounds were fully characterised by multinuclear NMR and IR spectroscopies, MS spectrometry and elemental analysis; the NMR spectroscopic data were used for structural assignment of the N-1 and N-2 isomers. The molecular structure of indazol-2-yl-acetic acid (5b) was determined by X-ray diffraction, which shows a supramolecular architecture involving O2-H...N1 intermolecular hydrogen bonds.

Proton conduction in 1H‐1,2,3‐triazole polymers: Imidazole‐like or pyrazole‐like?

“…Benzopyrazole has 1 H‐ and 2 H‐ tautomers. It is reasonable to suggest that the 2 H‐ tautomer is less stable, because the benzene ring in benzopyrazole system is in the quinonoid form 15. Therefore, the poor performance of BPy might be due to the restricted interconversion between 1 H‐ and 2 H‐ tautomers of benzopyrazole, which can severely impede the dynamics (formation and breaking) of hydrogen bonding and hence the proton transfer.…”

Recent Advances in Indazole-Containing Derivatives: Synthesis and Biological Perspectives

“…Indazole usually contains two tautomeric forms: 1 H -indazole and 2 H -indazole ( Figure 1 ). Since 1 H -indazole is more thermodynamically stable than 2 H -indazole, it is the predominant tautomer [ 2 ].…”

The Suzuki Reaction Applied to the Synthesis of Novel Pyrrolyl and Thiophenyl Indazoles

“…In the presence of cesium carbonate (Cs 2 CO 3 ), a 1.2:1 ratio of 3a and the N -2 isomer 3g was obtained. The two regioisomers were purified and identified by comparison of their spectral data with that reported for similar N -alkylated indazoles [ 31 ].…”