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Synthesis of indazoles

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Various N-aryl-1H-indazoles and benzimidazoles were synthesized from common arylamino oximes in good to excellent yields depending upon the base used in the reaction. Triethylamine promoted the formation of benzimidazoles, whereas 2-aminopyridine promoted the formation of N-arylindazoles.
B. C. Wray, J. P. Stambuli, Org. Lett., 2010, 12, 4576-4579.


CuI-catalyzed coupling of N-acyl-N′-substituted hydrazines with aryl iodides affords N-acyl-N′,N′-disubstituted hydrazines regioselectively. N-Acyl-N′-substituted hydrazines can also react with 2-bromoarylcarbonylic compounds in the presence of 4-hydroxy-L-proline as ligand to provide 1-aryl-1H-indazoles.
X. Xiong, Y. Jiang, D. Ma, Org. Lett., 2012, 14, 2552-2555.


1-Aryl-2-(2-nitrobenzylidene)hydrazines readily undergo intramolecular amination to afford 1-aryl-1H-indazole derivatives in good yields in the presence of potassium tert-butoxide in N,N-dimethylformamide at 100 C. Displacement of the nitro group was achieved in the absence of significant electron-withdrawing substituents.
F. Esmaeili-Marandi, M. Saeedi, M. Mahdavi, I. Yavari, A. Foroumadi, A. Shafiee, Synlett, 2014, 25, 2605-2608.


The 1H-indazole skeleton can be constructed by a [3 + 2] annulation approach from arynes and hydrazones. Under different reaction conditions, both N-tosylhydrazones and N-aryl/alkylhydrazones can be used to afford various indazoles.
P. Li, C. Wu, J. Zhao, D. C. Rogness, F. Shi, J. Org. Chem., 2012, 77, 3127-3133.


Readily available, stable, and inexpensive N-tosylhydrazones react with arynes under mild reaction conditions to afford 3-substituted indazoles in good yields. The reaction involves a 1,3-dipolar cycloaddition of in situ generated diazo compounds and arynes.
P. Li, J. Zhao, C. Wu, R. C. Larock, F. Shi, Org. Lett., 2011, 13, 3340-3343.


The [3+2] cycloaddition of a variety of diazo compounds with o-(trimethylsilyl)aryl triflates in the presence of CsF or TBAF at room temperature provides a very direct, efficient approach to a wide range of potentially biologically and pharmaceutically interesting substituted indazoles in good to excellent yields under mild reaction conditions.
Z. Liu, F. Shi, P. D. G. Martinze, C. Raminelli, R. C. Larock, J. Org. Chem., 2008, 73, 219-226.


A Cu-catalyzed coupling reaction of 2-halobenzonitriles with hydrazine carboxylic esters and N′-arylbenzohydrazides proceed smoothly to provide substituted 3-aminoindazoles through a cascade coupling-(deacylation-)condensation process. A wide range of substituted 3-aminoindazoles can be prepared from the corresponding coupling partners.
L. Xu, Y. Peng, Q. Pan, Y. Jiang, D. Ma, J. Org. Chem., 2013, 78, 3400-3401.


A Cu-catalyzed coupling reaction of 2-halobenzonitriles with hydrazine carboxylic esters and N′-arylbenzohydrazides proceed smoothly to provide substituted 3-aminoindazoles through a cascade coupling-(deacylation-)condensation process. A wide range of substituted 3-aminoindazoles can be prepared from the corresponding coupling partners.
L. Xu, Y. Peng, Q. Pan, Y. Jiang, D. Ma, J. Org. Chem., 2013, 78, 3400-3401.


A general two-step synthesis of substituted 3-aminoindazoles from 2-bromobenzonitriles involves a palladium-catalyzed arylation of benzophenone hydrazone followed by an acidic deprotection/cyclization sequence. This procedure offers a general and efficient alternative to the typical SNAr reaction of hydrazine with o-fluorobenzonitriles.
V. Lefebvre, T. Cailly, F. Fabis, S. Rault, J. Org. Chem., 2010, 75, 2730-2732.