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Synthesis of pyrazolines

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A one-pot synthesis of nitrogen-containing heterocycles from alkyl dihalides and primary amines and hydrazines occurs under microwave irradiation via a simple and efficient cyclocondensation in an alkaline aqueous medium.
Y. Ju, R. S. Varma, J. Org. Chem., 2006, 71, 135-141.


One-pot condensations of ketones, aldehydes and hydrazine monohydrochloride readily formed pyrazoline intermediates under mild conditions. In situ oxidation employing bromine afforded a wide variety of pyrazoles in very good yields. Alternatively, a more benign oxidation protocol affords 3,5-disubstituted or 3,4,5-trisubstituted pyrazoles by simply heating pyrazolines in DMSO under oxygen.
V. Lellek, C.-y. Chen, W. Yang, J. Liu, X. Ji, R. Faessler, Synlett, 2018, 29, 1071-1075.


Arylhydrazines regioselectively react with 3-butynol in the presence of a catalytic amount of zinc triflate to give aryl-substituted pyrazolines. The resulting products are easily oxidized in a one-pot procedure to the corresponding pyrazoles.
K. Alex, A. Tillack, N. Schwarz, M. Beller, Org. Lett., 2008, 10, 2377-2379.


A ligand-free, palladium-catalyzed aminoarylation of unactivated alkenes in β,γ-unsaturated hydrazones provides diversely substituted dihydropyrazoles in good yields via an efficient and simultaneous formation of C(sp3)-N and C(sp3)-C(sp2) bonds under mild conditions.
M.-N. Yang, D.-M. Yan, Q.-Q. Zhao, J.-R. Chen, W.-J. Xiao, Org. Lett., 2017, 19, 5208-5211.


Various 1-acyl-5-hydroxy-4,5-dihydro-1H-pyrazoles have been prepared in good yields from the corresponding 2-alkyn-1-ones. The resulting dihydropyrazoles undergo dehydration and iodination in the presence of ICl and Li2CO3 at room temperature to provide 1-acyl-4-iodo-1H-pyrazoles.
J. P. Waldo, S. Mehta, R. C. Larock, J. Org. Chem., 2008, 73, 6666-6670.


In situ formed 1,2-diaza-1,3-dienes were used in formal [4 + 1]-annulation reactions with fluorinated sulfur ylides to provide 5-(trifluoromethyl)pyrazolines in good yields.
Z. Wang, Y. Yang, F. Gao, Z. Wang, Q. Luo, L. Fang, Org. Lett., 2018, 20, 934-937.


A novel, efficient, and general domino reaction of 2-acylaziridines with the Huisgen zwitterions furnishes 2-pyrazolines. A possible mechanism for the domino sequence is proposed.
S.-L. Cui, J. Wang, Y.-G. Wang, Org. Lett., 2008, 10, 13-16.


A convenient copper-catalyzed intra-/intermolecular diamination of β,γ-unsaturated hydrazones with simple amines enables an efficient access to various nitrogen-containing pyrazolines under mild reaction conditions.
M. Chen, L.-J. Wang, P.-X. Ren, X.-Y. Hou, Z. Fang, M.-N. Han, W. Li, Org. Lett., 2018, 20, 510-513.