Synthesis of Difluoromethyl Pyrazolines and Pyrazoles by [3+2] Cycloaddition Reaction of Difluoroacetohydrazonoyl Bromides with Electron‐deficient Olefins

Ren, Yuanyuan; Ma, Ransong; Feng, Yang; Wang, Ke‐Hu; Wang, Junjiao; Huang, Danfeng; Lv, Xiaobo; Hu, Yulai

doi:10.1002/ajoc.202200438

Cited by 15 publications

(16 citation statements)

References 58 publications

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“…Based on additional experiments, a mechanistic scenario comprising acyl-transfer onto the surface of heterogeneous oxidant was proposed. The presented results extend the scope of the previously reported method for the synthesis of the title compounds in organic solvents [ 42 ] and supplements recent developments, both in the synthesis of pyrazoles [ 2 , 53 , 54 , 55 ] and the application of nitrile imines as building blocks for organic synthesis [ 17 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 56 , 57 , 58 , 59 ].…”

Section: Discussionsupporting

confidence: 87%

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

2022

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A solvent-free two-step synthesis of polyfunctionalized pyrazoles under ball-milling mechanochemical conditions was developed. The protocol comprises (3 + 2)-cycloaddition of in situ generated nitrile imines and chalcones, followed by oxidation of the initially formed 5-acylpyrazolines with activated MnO2. The second step proceeds via an exclusive deacylative pathway, to give a series of 1,4-diarylpyrazoles functionalized with a fluorinated (CF3) or non-fluorinated (Ph, COOEt, Ac) substituent at C(3) of the heterocyclic ring. In contrast, MnO2-mediated oxidation of a model isomeric 4-acylpyrazoline proceeded with low chemoselectivity, leading to fully substituted pyrazole as a major product formed via dehydrogenative aromatization. The presented approach extends the scope of the known methods carried out in organic solvents and enables the preparation of polyfunctionalized pyrazoles, which are of general interest in medicine and material sciences.

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Section: Discussionsupporting

confidence: 87%

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

2022

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“…The reaction is also applicable to α , β ‐unsaturated esters, and amides. It is interesting to note that the process is substrate‐controlled because CF 2 H‐functionalized pyrazoles are the products when β ‐nitroolefins are used instead, under the same mild conditions [14] …”

Section: 3‐dipolar Cycloadditionsmentioning

confidence: 99%

“…It is interesting to note that the process is substrate-controlled because CF 2 H-functionalized pyrazoles are the products when β-nitroolefins are used instead, under the same mild conditions. [14] Nitrile imines have also been shown to react with 3-methyleneindolinones to afford spiro-pyrazolines. Following their publication on the synthesis of analogous spiro-isoxazolines via [3 + 2]-cycloaddition reaction between nitrile oxides and 3-methylene oxindoles 9, [15a] Roth et al investigated the application of nitrile iminoesters 8 to this reaction.…”

Section: Cycloadditions With αβ-Enones As Dipolarophilesmentioning

confidence: 99%

Strategies and Methods for the Synthesis of 2‐Pyrazolines: Recent Developments (2012–2022)

Matiadis

2023

Adv Synth Catal

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2‐Pyrazolines are important five‐membered heterocycles, containing two adjacent nitrogen atoms. They can incorporate various functional groups and possess unique biological properties. Moreover, they have been used as useful building blocks. In recent years, the field of 2‐pyrazoline synthesis has experienced enormous progress. Novel strategies have been developed, and many studies reporting improvements or adaptations of existing protocols have been published, giving access to new functionalizations, unexplored structures, and/or enantioselective synthesis. This review summarizes the progress made in synthetic methodologies during the period from 2012 to 2022. The functionalization challenges and capabilities, scopes and limitations of the reactions, substitution patterns, and mechanisms of the reactions, where appropriate, will be discussed.

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“…On the other hand, a number of more recent publications reported on nitrile imines functionalized at the C -termini with either CF 3 [ 25 , 26 , 27 , 28 , 29 , 30 ] or CF 2 H [ 31 , 32 ] groups. They were successfully applied for the synthesis of various 5-membered N -heterocyclic systems formed via (3+2)-cycloadditions, notably, with most of the cases proceeding in a fully regioselective manner.…”

Section: Introductionmentioning

confidence: 99%

Trifluoromethylated 4,5-Dihydro-1,2,4-triazin-6(1H)-ones via (3+3)-Annulation of Nitrile Imines with α-Amino Esters

et al. 2023

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The synthesis of two series of monocyclic and bicyclic trifluoromethylated 4,5-dihydro-1,2,4-triazin-6(1H)-one derivatives based on (3+3)-annulation of methyl esters derived from natural α-amino acids with in situ generated trifluoroacetonitrile imines has been described. The devised protocol is characterized by a wide scope, easily accessible substrates, remarkable functional group tolerance, and high chemical yield. In reactions with chiral starting materials, no racemization at the stereogenic centers was observed and the respective enantiomerically pure products were obtained. Selected functional group interconversions carried out under catalytic hydrogenation and mild PTC oxidation conditions were also demonstrated.

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Synthesis of Difluoromethyl Pyrazolines and Pyrazoles by [3+2] Cycloaddition Reaction of Difluoroacetohydrazonoyl Bromides with Electron‐deficient Olefins

Cited by 15 publications

References 58 publications

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

Fluorinated and Non-Fluorinated 1,4-Diarylpyrazoles via MnO2-Mediated Mechanochemical Deacylative Oxidation of 5-Acylpyrazolines

Strategies and Methods for the Synthesis of 2‐Pyrazolines: Recent Developments (2012–2022)

Trifluoromethylated 4,5-Dihydro-1,2,4-triazin-6(1H)-ones via (3+3)-Annulation of Nitrile Imines with α-Amino Esters

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