New advances in asymmetric organocatalysis II

• Radovan Šebesta

Beilstein J. Org. Chem. 2025, 21, 766–769, doi:10.3762/bjoc.21.60

• describes the enantioselective Michael addition of pyrazoline-5-ones to α,β-unsaturated ketones. The enantioselectivity and chemical efficiency of this transformation were achieved with a cinchona-alkaloid-derived primary-amine–Brønsted acid composite [22]. A good demonstration of how organocatalysis

Unraveling aromaticity: the dual worlds of pyrazole, pyrazoline, and 3D carborane

• Zahra Noori,
• Miquel Solà,
• Clara Viñas,
• Francesc Teixidor and
• Jordi Poater

Beilstein J. Org. Chem. 2025, 21, 412–420, doi:10.3762/bjoc.21.29

• a π system with 6 π electrons [11]. When fused with a benzene ring, sharing a C–C bond, it remains aromatic, which is the case of indazole. Pyrazoline (C3H6N2), similar to pyrazole, formally has only one double bond and a lone pair on the nitrogen, so it does not satisfy Hückel's rule and it is

• therefore non-aromatic. Even when fused with benzene via a C–C bond, pyrazoline remains non-aromatic, which is the case of indazoline. Icosahedral carboranes are globular molecular clusters made of carbon and boron, displaying 3D aromaticity [12][13][14][15]. Their unique properties – such as aromaticity

• be assigned to an aromatic C–C bond (that of benzene is 1.394 Å, computed at the same level of theory). Noticeably, highly diagnostic are also the NN bond lengths. In the aromatic indazole and pyrazole this NN distance is near 1.35 Å, whereas it is longer near 1.46 Å for the non-aromatic 3-pyrazoline

Multicomponent syntheses of pyrazoles via (3 + 2)-cyclocondensation and (3 + 2)-cycloaddition key steps

• Ignaz Betcke,
• Alissa C. Götzinger,
• Maryna M. Kornet and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2024, 20, 2024–2077, doi:10.3762/bjoc.20.178

• feature of the method is the regioselectivity with asymmetric diketones. In addition to β-ketoesters, acetylacetone can be used in the concept. The same research group employed ethyl 4,4,4-trifluoroacetoacetate as a substrate in this method. The pyrazoline oxidation proved to be critical, and the addition

• pyrazoline, which leads to increased yields. In addition to fully substituted pyrazoles, bispyrazoles can also be synthesized [97]. Other Lewis acid catalysts employed in this method include chloride-functionalized silica gel (SiO2Cl) [98] and Sc(OTf)3 [99]. Importantly, all reactions of this method are

Harnessing the versatility of hydrazones through electrosynthetic oxidative transformations

• Aurélie Claraz

Beilstein J. Org. Chem. 2024, 20, 1988–2004, doi:10.3762/bjoc.20.175

• this procedure involved the (3 + 2)-cycloaddition reaction between electrogenerated diphenyldiazomethane and methyl acrylate delivering the corresponding pyrazoline in good yield (68%). Olefins are highly common structural motifs in natural and synthetic organic compounds. They are also often employed

(E,Z)-1,1,1,4,4,4-Hexafluorobut-2-enes: hydrofluoroolefins halogenation/dehydrohalogenation cascade to reach new fluorinated allene

• Nataliia V. Kirij,
• Andrey A. Filatov,
• Yurii L. Yagupolskii,
• Sheng Peng and
• Lee Sprague

Beilstein J. Org. Chem. 2024, 20, 452–459, doi:10.3762/bjoc.20.40

• the formation of the corresponding olefin [12]. Another area of application of olefins 1a,b is based on C=C double bond addition reactions. As early as 1968, Atherton and Fields showed that (Z)- and (E)-butenes 1a,b reacted with diazotrifluoroethane to give 3,4,5-tris(trifluoromethyl)pyrazoline [13

Trifluoromethylated hydrazones and acylhydrazones as potent nitrogen-containing fluorinated building blocks

• Zhang Dongxu

Beilstein J. Org. Chem. 2023, 19, 1741–1754, doi:10.3762/bjoc.19.127

• activation [108][109][110]. Besides, pyrazolidine and pyrazoline compounds are highly valuable hereocycles which are found in many natural products and bioactive compounds. Among them, CF3-substituted pyrazolidines have already been shown to be highly bioactive [111][112][113]. Thus, Hu et al. chose

Recent advances in organocatalytic asymmetric aza-Michael reactions of amines and amides

• Pratibha Sharma,
• Raakhi Gupta and
• Raj K. Bansal

Beilstein J. Org. Chem. 2021, 17, 2585–2610, doi:10.3762/bjoc.17.173

• synthesis of dihydro-β-carbolines. Asymmetric aza-Michael synthesis of N-substituted 2-pyridones. Asymmetric aza-Michael–Henry cascade reaction. Asymmetric aza-Michael addition for the formation of (S)-(−)-pyrazoline. Asymmetric aza-Michael addition reaction catalyzed by phase-transfer catalyst. Asymmetric

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• C60 or b) possible formation of both isomers as a result of 1,3-dipolar cycloaddition of the diazo compound to the fullerene, followed by elimination of molecular nitrogen from the pyrazoline intermediate. Second, the rearrangement of [5,6]-open isomers into thermodynamically more stable [6,6]-closed

• ethereal solution of diazomethane in toluene at 0 °C resulted in pyrazoline derivative C [81]. The adduct isolated chromatographically was exposed to ultraviolet (UV) irradiation for 25 min at 25 °C in a quartz tube. The resulting isomers 3 and 4 were separated by reversed-phase high-performance liquid

• fullerene based on diazo compounds allows us to state the following: An alternative to the synthesis of methanofullerenes by the Bingel methodology is provided by the thermal [2 + 1] cycloaddition of diazo compounds to the fullerene. Then follows the photolysis or thermolysis of pyrazoline intermediates by

Control over size, shape, and photonics of self-assembled organic nanocrystals

• Chen Shahar,
• Yaron Tidhar,
• Yunmin Jung,
• Haim Weissman,
• Sidney R. Cohen,
• Ronit Bitton,
• Iddo Pinkas,
• Gilad Haran and
• Boris Rybtchinski

Beilstein J. Org. Chem. 2021, 17, 42–51, doi:10.3762/bjoc.17.5

• devices [4][5][6]. The development of the reprecipitation method [7] allowed the facile fabrication of (often crystalline) organic nano- and microparticles based on polydiacetylene [8], pyrazoline [9], perylene [10], and other molecules. In several cases, size-dependent absorption was reported [11][12][13

Selective and reversible 1,3-dipolar cycloaddition of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with 1,3-diphenylprop-2-en-1-ones under microwave irradiation

• Alexander P. Molchanov,
• Mariia M. Efremova,
• Mariya A. Kryukova and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2020, 16, 2679–2686, doi:10.3762/bjoc.16.218

• product from a substantial quantity of formed pyrazoline 4c. It is remarkable that the reaction of 6-phenyl-1,5-diazabicyclo[3.1.0]hexane (1a) with diarylpropenone 2f under the same conditions (microwave irradiation, 110 °С, toluene, 3 h) affords the two adducts 3f and 3m in a 1:2 ratio and the two

• polar species in the ionic medium. Therefore, we carried out the reaction of DABCH 1a with propenone 2f in bmimCl in the presence of BF3·Et2O at 80 °C for 8 h, that led to the formation of adduct 3m and pyrazoline 4a. The reaction of DABCH 1b and propenone 2a under the same conditions resulted in the

• formation of adduct 3m and pyrazoline 4b (Scheme 3). Thus, the azomethine imine A, formed by heating of DABCH 1a, either reacts with propenone 2f giving the adduct 3m or undergoes isomerization affording pyrazoline 4a. On the basis of this observation we suppose that the reaction products undergo

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

• Guillaume Ernouf,
• Jean-Louis Brayer,
• Christophe Meyer and
• Janine Cossy

Beilstein J. Org. Chem. 2019, 15, 333–350, doi:10.3762/bjoc.15.29

• -Δ1-pyrazoline [39]) or by pyrolysis of the sodium salt of 3-propionyloxytetramethylcyclobutanone tosyl hydrazone [40]. It is also worth mentioning that completely divergent reactivities have also been reported for cyclopropenylcarbinyl esters in the presence of transition metal catalysts [41][42

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• tropone unit: In 1975, Franck-Neumann and Martina reported the reaction of dimethyl diazomethane with tropone and benzotropones [83]. This reaction gave benzo-4,5-dimethyl-8,8-cyclooctatrienone (94, 30% isolable yield) as an insertion product via a carbonyl group and pyrazoline 95 as 1,3-dipolar addition

Hypervalent iodine-mediated Ritter-type amidation of terminal alkenes: The synthesis of isoxazoline and pyrazoline cores

• Sang Won Park,
• Soong-Hyun Kim,
• Jaeyoung Song,
• Ga Young Park,
• Darong Kim,
• Tae-Gyu Nam and
• Ki Bum Hong

Beilstein J. Org. Chem. 2018, 14, 1028–1033, doi:10.3762/bjoc.14.89

• alkene functionalization utilizing a PhI(OAc)2 ((diacetoxyiodo)benzene, PIDA)/Lewis acid combination in order to access isoxazoline and pyrazoline cores. Based on allyl ketone oximes and allyl ketone tosylhydrazones, we have developed an alkene oxyamidation and amido-amidation protocol en route to

• accessing both isoxazoline and pyrazoline cores. Additionally, acetonitrile serves as both the solvent and an amine source in the presence of this PIDA/Lewis acid combination. This operationally straightforward and metal-free protocol provides an easy access to isoxazoline and pyrazoline derivatives

• . Keywords: amido-amidation; hypervalent iodine; isoxazoline; metal-free; oxyamidation; pyrazoline; Introduction Isoxazoline and pyrazoline-containing heterocycles are abundant in natural products and biologically active molecules [1][2][3][4][5]. Thus, these scaffolds are also important from the standpoint

Derivatives of the triaminoguanidinium ion, 5. Acylation of triaminoguanidines leading to symmetrical tris(acylamino)guanidines and mesoionic 1,2,4-triazolium-3-aminides

• Jan Szabo,
• Julian Greiner and
• Gerhard Maas

Beilstein J. Org. Chem. 2017, 13, 579–588, doi:10.3762/bjoc.13.57

• went on to a 3,6-di(pyrazol-1-yl)-1,2,4,5-tetrazine [11], and with 1,1,1-trifluoro-2,4-pentanedione two branches of TAG-Cl were converted into pyrazoline moieties and the third one into an enaminone [12]. Not much is known about the acylation of triaminoguanidines. Reactions with carboxylic acids have

Multicomponent reactions: A simple and efficient route to heterocyclic phosphonates

• Mohammad Haji

Beilstein J. Org. Chem. 2016, 12, 1269–1301, doi:10.3762/bjoc.12.121

• this reaction, the generated diazomethyl anion 215 underwent a 1,3-dipolar cycloaddition with α,β-unsaturated aldehydes 231 to give pyrazolinecarboxaldehyde 232. The subsequent reaction of aldehyde 232 with another molecule of BOR afforded pyrazoline alkyne intermediate 233 which, after a 1,3-hydrogen

Conjugate addition–enantioselective protonation reactions

• James P. Phelan and
• Jonathan A. Ellman

Beilstein J. Org. Chem. 2016, 12, 1203–1228, doi:10.3762/bjoc.12.116

• nucleophiles 111, which all reacted with high enantioselectivity, including pyrazoline 111e (Scheme 26b). Organocatalysts Building on their earlier work with α,β-unsaturated aldehydes (vide infra), Luo and Cheng have extensively explored the use of enamine catalysis for conjugate addition–enantioselective

Synthesis of enones, pyrazolines and pyrrolines with gem-difluoroalkyl side chains

• Assaad Nasr El Dine,
• Ali Khalaf,
• Danielle Grée,
• Olivier Tasseau,
• Fares Fares,
• Nada Jaber,
• Philippe Lesot,
• Ali Hachem and
• René Grée

Beilstein J. Org. Chem. 2013, 9, 1943–1948, doi:10.3762/bjoc.9.230

• possibility of using these molecules as scaffolds for the preparation of focused chemical libraries. In order to explore this possibility we developed representative examples of Pd-catalyzed reactions starting from p-bromo derivatives 4e and 6e. The results are given in Scheme 7 for pyrazoline 4e. Suzuki

Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

• Zhi-Cong Geng,
• Jian Chen,
• Ning Li,
• Xiao-Fei Huang,
• Yong Zhang,
• Ya-Wen Zhang and
• Xing-Wang Wang

Beilstein J. Org. Chem. 2012, 8, 1710–1720, doi:10.3762/bjoc.8.195

• , 28.19; IR (KBr) νmax: 3354.8, 2980.4, 2934.2, 2854.2, 1728.7, 1705.9, 1600.2, 1518.9, 1456.0, 1367.7, 1345.9, 1311.6, 1243.1, 1145.0, 990.9, 853.5, 758.4 cm−1; HRMS–ESI (m/z): [Na]+ calcd for C19H27N3O7, 432.1741; found, 432.1724. Important heterocycles containing pyrazolidine or pyrazoline structures

Chemistry of polyhalogenated nitrobutadienes, 10: Synthesis of highly functionalized heterocycles with a rigid 6-amino-3-azabicyclo[3.1.0]hexane moiety

• Viktor A. Zapol’skii,
• Jan C. Namyslo,
• Armin de Meijere and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2012, 8, 621–628, doi:10.3762/bjoc.8.69

• results in the diaminobutadiene II, which tautomerizes to the stable amidine III. The pyrazoline IV is then formed by an intramolecular SNVin reaction. Finally, HCl elimination affords the pyrazoles 27, 28. The stimulus to investigate such compounds originated from the known pharmacological activities of

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

• Kristina Butković,
• Željko Marinić,
• Krešimir Molčanov,
• Biserka Kojić-Prodić and
• Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

• ] or photochemically [8][9][10][11][12][13][14][15][16][17], giving different pyrazole and/or pyrazoline derivatives, depending on the applied dipolarophile (Scheme 1). Namely, sydnones are masked 1,3-dipoles that by photolysis give nitrile imine intermediates, or in thermal reactions react as cyclic

• result of competitive photolysis of the sydnone moiety was confirmed on irradiation of 1 in the presence of acrolein and isolation of the pyrazoline derivative (F, Figure 3) [17]. In the case of stilbenylsydnones 2, where the sydnone moiety is directly connected to the ortho position of the stilbene, the

Ugi post-condensation copper-triggered oxidative cascade towards pyrazoles

• Aurélie Dos Santos,
• Laurent El Kaim,
• Laurence Grimaud and
• Caroline Ronsseray

Beilstein J. Org. Chem. 2011, 7, 1310–1314, doi:10.3762/bjoc.7.153

• triggered either by copper acetate or acetic acid [24][25][26][27][28][29]. The resulting pyrazoline A may be oxidized by copper(II) salts forming intermediate D after addition of water [30][31]. Two alternative paths may then be observed from D: Ring-opening leading to azo or hydrazono derivatives such as

Approaches towards the synthesis of 5-aminopyrazoles

• Ranjana Aggarwal,
• Vinod Kumar,
• Rajiv Kumar and
• Shiv P. Singh

Beilstein J. Org. Chem. 2011, 7, 179–197, doi:10.3762/bjoc.7.25

• which slowly cyclizes to afford 2,3-dihydro-1H-pyrazoles 113 in good yields. 4-Trifluoromethylphenylhydrazine also adds to ethylene 111 (X = CO2Et), however, the resulting adduct 112 is formed primarily as a single diastereomer and does not undergo intramolecular cyclization to pyrazoline 113 even in

• refluxing benzene. Further, the reaction of isomeric alkene 115 with an arylhydrazine initially forms the unstable pyrazoline 116 that transforms into pyrazole 118. Firstly, the C–P bond apparently undergoes hydrolysis and the resulting 117 is slowly oxidized by atmospheric oxygen to yield pyrazole 118

The tert- amino effect in heterocyclic chemistry: Synthesis of new fused pyrazolinoquinolizine and 1,4-oxazinopyrazoline derivatives

• Dipak Prajapati and
• Kalyan Jyoti Borah

Beilstein J. Org. Chem. 2007, 3, No. 43, doi:10.1186/1860-5397-3-43

• characterized fully by high resolution spectral analysis (see Supporting Information File 1 &Supporting Information File 2 for full experimental and spectral data). We then reacted chloroformyl pyrazoline 2 with pyrrolidine and morpholine to get the corresponding tert-amino derivatives 3. The olefinic products

An improved synthesis of 1,3,5-triaryl- 2-pyrazolines in acetic acid aqueous solution under ultrasound irradiation

• Ji-Tai Li,
• Xiao-Hui Zhang and
• Zhi-Ping Lin

Beilstein J. Org. Chem. 2007, 3, No. 13, doi:10.1186/1860-5397-3-13

• Ji-Tai Li Xiao-Hui Zhang Zhi-Ping Lin College of Chemistry and Environmental Science, Hebei University; Key Laboratory of Analytical Science and Technology of Hebei Province, Baoding 071002, P. R. China 10.1186/1860-5397-3-13 Abstract Background Pyrazoline derivatives have been found to possess a

• broad spectrum of biological activities. Among various pyrazoline derivatives, 2-pyrazolines seem to be the most frequently studied. A variety of methods have been reported for the preparation of this class of compound. However, in spite of their potential utility, some of the reported methods suffer

• solution at room temperature under ultrasound irradiation. Background Pyrazoline derivatives have been found to possess a broad spectrum of biological activities such as tranquillizing, muscle relaxant, psychoanaleptic, anticonvulsant, antihypertensive, and antidepressant activities. [1][2][3][4][5][6