21985-07-9Relevant articles and documents
Denitrative imino-diaza-Nazarov cyclization: Synthesis of pyrazoles
Aegurla, Balakrishna,Jarwal, Nisha,Peddinti, Rama Krishna
, p. 6100 - 6107 (2020/10/21)
An iodine-catalyzed denitrative imino-diaza-Nazarov cyclization (DIDAN) methodology has been developed for the synthesis of pyrazoles with high to excellent yields by using α-nitroacetophenone derivatives and in situ generated hydrazones. The key transformation of this oxidative 4π-electrocyclization proceeds through an enamine-iminium ion intermediate. This rapid one-pot DIDAN protocol results in the selective generation of C-C and C-N bonds and cleavage of a C-N bond. This journal is
Sunlight-promoted Direct Irradiation of N-centred Anion: The Photocatalyst-free Synthesis of Pyrazoles in Water
Zhang, Te,Meng, Yunge,Lu, Jinye,Yang, Yuting,Li, Gong-Qiang,Zhu, Chunyin
supporting information, p. 3063 - 3068 (2017/12/04)
A practical method through sunlight mediated annulation of α,β-unsaturated hydrazones has been developed for the synthesis of pyrazole. Based on the analysis of UV-Vis absorption of the substrate, the reaction was designed to avoid the use of external photocatalysis and proceeds via direct irradiation of N-centred anion by sunlight. The key features of this reaction include operational simplicity, readily available reagents, and amenability to gram-scale synthesis. (Figure presented.).
An Efficient Synthesis of Substituted Pyrazoles from One-Pot Reaction of Ketones, Aldehydes, and Hydrazine Monohydrochloride
Lellek, Vit,Chen, Cheng-Yi,Yang, Wanggui,Liu, Jie,Ji, Xuebao,Faessler, Roger
supporting information, p. 1071 - 1075 (2018/02/26)
An efficient, one-pot and metal-free process for the preparation of 3,5-disubstituted and 3,4,5-trisubstituted pyrazoles on multi-gram scale was developed. One-pot condensation of ketones, aldehydes and hydrazine monohydrochloride readily formed pyrazoline intermediates under mild conditions. Oxidation of pyrazolines, in situ, employing bromine afforded a wide variety of pyrazoles. The methodology offers a fast, and often chromatography-free protocol for the synthesis of 3,4,5-substituted pyrazoles in good to excellent 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.
The diaza-Nazarov cyclization involving a 2,3-diaza-pentadienyl cation for the synthesis of polysubstituted pyrazoles
Aegurla, Balakrishna,Peddinti, Rama Krishna
, p. 9643 - 9652 (2017/11/30)
An unprecedented iodine-mediated diaza-Nazarov (DAN) type cyclization for the construction of substituted pyrazoles from easily available starting materials via an enamine-iminium ion intermediate is described. The oxidative cyclization worked under green conditions with remarkable regioselectivity. This one-pot, efficient and operationally simple three-component intramolecular regioselective DAN cyclization displayed a wide range of substrate scope. The dichotomy of reaction pathways has been explored with density functional theory in the gas phase and solution phase. Of the possible 1,5-, 1,6-, and 1,7-electrocyclizations, the DAN cyclization, i.e., the 1,5-pathway offers the lowest activation energy barrier supporting our experimental observations.
A facile and expeditious approach to substituted 1H-pyrazoles catalyzed by iodine
Zhang, Hailei,Wei, Qian,Zhu, Guodong,Qu, Jingping,Wang, Baomin
supporting information, p. 2633 - 2637 (2016/06/01)
A facile and expeditious method for the synthesis of 1H-pyrazoles by the reaction of α,β-unsaturated aldehydes/ketones and sulfonyl hydrazide catalyzed by as low as 2 mol % I2 has been demonstrated. This synthetic system features simple operation and mild reaction conditions, and displays a broad functional group tolerance furnishing good to excellent yields.
Phosphine- and copper-free palladium catalyzed one-pot four-component carbonylation reaction for the synthesis of isoxazoles and pyrazoles
Iranpoor, Nasser,Firouzabadi, Habib,Etemadi-Davan, Elham
supporting information, p. 837 - 840 (2016/02/05)
The palladium catalyzed one-pot synthesis of isoxazoles and pyrazoles from aryl iodides, terminal alkynes, chromium hexacarbonyl and hydroxylamine hydrochloride or aqueous hydrazine solution is described. The Sonogashira carbonylative coupling intermediate was trapped in situ by hydroxylamine hydrochloride or aqueous hydrazine to deliver isoxazoles or pyrazoles, respectively, in high yields. This efficient method proceeds at atmospheric pressure and moderate temperature and does not require the use of copper, phosphine ligands or gaseous carbon monoxide.
A highly efficient heterogeneous palladium-catalyzed cascade three-component reaction of acid chlorides, terminal alkynes and hydrazines leading to pyrazoles
Chen, Qiurong,Yao, Fang,Yin, Lin,Cai, Mingzhong
, p. 108 - 113 (2016/01/15)
In the presence of 0.5 mol% of 3-(2-aminoethylamino)propyl-functionalized MCM-41-immobilized palladium(II) complex [MCM-41-2N-Pd(OAc)2] and 1.0 mol% of CuI, acid chlorides were coupled with terminal alkynes in Et3N at 50 °C to give α,β-unsaturated ynones, which were converted in situ into pyrazoles by the cycloaddition of hydrazines at room temperature with acetonitrile as cosolvent. The cascade reactions generated a variety of pyrazole derivatives in moderate to good yields, and this heterogeneous palladium catalyst exhibited higher catalytic activity than PdCl2(PPh3)2 and could be recovered and reused for at least 10 consecutive trials without any decreases in activity.
Synthesis of 3,5-disubstituted-1H-pyrazoles from acid chlorides, alkynes, and hydrazine in the presence of silica-supported-zinc bromide
Keivanloo, Ali,Bakherad, Mohammad,Samangooei, Shahrzad
, p. 484 - 486 (2015/11/03)
An efficient one-pot palladium- And copper-free procedure has been developed for a convenient synthesis of 3,5-disubstituted-1H-pyrazoles from various acid chlorides, terminal alkynes and hydrazine by a coupling reaction and cyclocondensation sequence. Acid chlorides react with terminal alkynes in the presence of silica-supported-zinc bromide to give α,β-unsaturated ynones, and in situ conversion into pyrazoles by the hydrazine cyclocondensation.
Preparation of 3,5-disubstituted pyrazoles and isoxazoles from terminal alkynes, aldehydes, hydrazines, and hydroxylamine
Harigae, Ryo,Moriyama, Katsuhiko,Togo, Hideo
, p. 2049 - 2058 (2014/04/03)
The reaction of terminal alkynes with n-BuLi, and then with aldehydes, followed by the treatment with molecular iodine, and subsequently hydrazines or hydroxylamine provided the corresponding 3,5-disubstituted pyrazoles or isoxazoles in good yields with high regioselectivity, through the formations of propargyl secondary alkoxides and α-alkynyl ketones. The present reactions are one-pot preparation of 3,5-disubstituted pyrazoles from terminal alkynes, aldehydes, molecular iodine, and hydrazines, and 3,5-disubstituted isoxazoles from terminal alkynes, aldehydes, molecular iodine, and hydroxylamine.
Copper on iron promoted one-pot synthesis of β-aminoenones and 3,5-disubstituted pyrazoles
Kovács, Szabolcs,Novák, Zoltán
, p. 8987 - 8993 (2013/09/24)
The reaction of hydroximoyl chlorides with acetylenes in the presence of a copper on iron bimetallic system leads to β-aminoenones via reductive ring opening of isoxazole intermediates. The valuable β-aminoenone building blocks can be isolated or transformed into pyrazoles with the addition of hydrazine in a straightforward one-pot procedure.
