Synthesis of trifluoromethyl-substituted pyrazolo[4,3-c]pyridines – sequential versus multicomponent reaction approach

• Barbara Palka,
• Angela Di Capua,
• Maurizio Anzini,
• Gyté Vilkauskaité,
• Algirdas Šačkus and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2014, 10, 1759–1764, doi:10.3762/bjoc.10.183

• . Oximes derived from (intermediate) 5-alkynyl-1-phenyl-3-trifluoromethyl-1H-pyrazole-4-carbaldehydes were transformed into the corresponding 1H-pyrazolo[4,3-c]pyridine 5-oxides by silver triflate-catalyzed cyclization. Detailed NMR spectroscopic investigations (1H, 13C, 15N and 19F) were undertaken with

• pyrazole-derived compounds the COX-2 inhibitor Celecoxib (Celebrex®) is an important representative (Figure 1) [7]. In continuation of our program regarding the synthesis of fluoro- and trifluoromethyl-substituted pyrazoles and annulated pyrazoles [8][9] we here present the synthesis of trifluoromethyl

• the pyrazolo[4,3-c]pyridine system can be mainly achieved through two different approaches. One strategy involves the annelation of a pyrazole ring onto an existing, suitable pyridine derivative [16]. Alternatively, the bicyclic system can be accessed by pyridine-ring formation with an accordant

Chemistry of polyhalogenated nitrobutadienes, 14: Efficient synthesis of functionalized (Z)-2-allylidenethiazolidin-4-ones

• Viktor A. Zapol’skii,
• Jan C. Namyslo,
• Mimoza Gjikaj and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2014, 10, 1638–1644, doi:10.3762/bjoc.10.170

• -inhibiting and antialgal properties [49], show anticancer activity [50][51], and are inhibitors of bacterial enzyme synthetase MurD with E. coli [52]. Additional treatment of thiazolidin-4-one 8 with a fivefold excess of hydrazine hydrate resulted in the formation of a 1H-pyrazole: A total of two hydrazine

• molecules were incorporated into the final product, whereas two additional equivalents were consumed capturing hydrochloric acid. In this way, the 1H-pyrazole 27 with an exceptional substitution pattern was obtained in 64% yield. The same reaction was applied to 5-arylmethylidene-thiazolidin-4-one 25 which

• furnished the corresponding 1H-pyrazole 28 in 52% yield (Scheme 5). A plausible multistep mechanism of this conversion is shown in Scheme 6: Initially, a first molecule of the strong nucleophile hydrazine is assumed to substitute the single C–Cl group within the trichlorovinyl subunit of 8 to give the

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

• Carla I. Nieto,
• Pilar Cabildo,
• M. Ángeles García,
• Rosa M. Claramunt,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2014, 10, 1620–1629, doi:10.3762/bjoc.10.168

• are: TC = 277.5 K and Δν = 0.12 ppm = 48 Hz; from them and using the Eyring equation [ΔG‡TC = 19.12 × TC × (10.32 + log TC/kC)] [32], we obtained: kC = 67.88 s−1 and ΔG‡277.5 = 58.0 kJ·mol−1. This barrier is similar to that of pyrazole in the same solvent (58.6 kJ·mol−1 at 289 K) [33]. The effect of

Regioselective S_N2' Mitsunobu reaction of Morita–Baylis–Hillman alcohols: A facile and stereoselective synthesis of α-alkylidene-β-hydrazino acid derivatives

• Silong Xu,
• Jian Shang,
• Junjie Zhang and
• Yuhai Tang

Beilstein J. Org. Chem. 2014, 10, 990–995, doi:10.3762/bjoc.10.98

• nitrogen-containing heterocyclic compounds, especially pyrazole derivatives [2][3][4][5][6][7]. Although various methods detailing the synthesis of hydrazines have been established [8], the development of an efficient synthesis of hydrazines with highly structural diversity from simple starting materials

• ). To further investigate the scope, a single case using allenic MBH alcohol 6 as the substrate was studied (Scheme 3). However, under similar conditions, the reaction between alcohol 6, tert-butyl azodicarboxylate (2c), and PPh3 afforded an interesting 1H-pyrazole compound 7 in 58% yield. A possible

• silica gel (gradient eluant: petroleum ether/ethyl acetate 9:1–3:1) to afford the hydrazines 3. Synthesis of 1H-pyrazole 7 Under N2 atmosphere and at room temperature, PPh3 (157 mg, 0.6 mmol) was slowly added to a stirred solution of allenic MBH alcohol 6 (61 mg, 0.3 mmol) and di-tert-butyl

Dimerisation, rhodium complex formation and rearrangements of N-heterocyclic carbenes of indazoles

• Zong Guan,
• Jan C. Namyslo,
• Martin H. H. Drafz,
• Martin Nieger and
• Andreas Schmidt

Beilstein J. Org. Chem. 2014, 10, 832–840, doi:10.3762/bjoc.10.79

• . Keywords: E/Z isomerism; indazol-3-ylidene; mesomeric betaine; pyrazole; quinazoline; Rh complex; Introduction As a result of their biochemical and pharmacological significance, there has been a considerably growing interest in indazoles in recent years, which is reflected in several book chapters and

• organocatalysts [15][16]. The N-heterocyclic carbenes of indazole (and pyrazole [17][18]), however, have a chemistry of their own which set them apart from the NHCs of the aforementioned ring systems. Portions of that field have been covered in recent review articles [18][19]. The N-heterocyclic carbene of

• observable in NMR spectra at standard temperature conditions. The spiro compound 14c crystallized from a saturated solution in n-hexane so that we were able to perform a single crystal X-ray analysis. The compound crystallized monoclinic. As expected, neither the pyrrole ring nor the pyrazole ring is planar

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• tautomerism and supramolecular structure. A reverse addition of the reagents led to the isolation of two novel products, namely bis-enehydrazines 6 with an unsymmetrical arrangement of the formally equivalent subunits. Keywords: bis-enehydrazines; enol ethers; NMR; pyrazole; tautomerism; Introduction Enol

• are shown in Scheme 3. It is well known that the reaction of hydrazine hydrate with alkoxymethylidenemalononitrile affords 3-amino-1H-pyrazole-4-carbonitrile (5a) [8][9][10][11][12][13]. Eight tautomeric forms of 5a could theoretically be expected (Figure 1). Five of these tauromeric forms carry an

• numbering and the fourth and fifth numbers giving the positions of two hydrogens. When dimethyl methoxymethylidenemalonate (3b) is used, methyl 3-hydroxy-1H-pyrazole-4-carboxylate (5b) is formed. Analogously, reaction of diethyl ethoxymethylenemalonate (3c) gives the corresponding ethyl 3-hydroxy-1H

Isocyanide-based multicomponent reactions towards cyclic constrained peptidomimetics

• Gijs Koopmanschap,
• Eelco Ruijter and
• Romano V.A. Orru

Beilstein J. Org. Chem. 2014, 10, 544–598, doi:10.3762/bjoc.10.50

• pyrazolones The group of Krasavin prepared both pyrazole- as well as pyrazolone-containing peptidomimetics via a sequential hydrazino-Ugi/Paal–Knorr condensation [94]. In their first approach, pyrazoles were obtained in good yields, however, with a limited scope of the condensation substrates (Scheme 32

Aminofluorination of 2-alkynylanilines: a Au-catalyzed entry to fluorinated indoles

• Antonio Arcadi,
• Emanuela Pietropaolo,
• Antonello Alvino and
• Véronique Michelet

Beilstein J. Org. Chem. 2014, 10, 449–458, doi:10.3762/bjoc.10.42

• in 75% yield (Table 1, entry 9). The addition of NaHCO3 [20][33] as a base to the reaction mixture failed to give 2a, whereas it was successful for the preparation of fluorinated pyrazole, via the gold(I)-catalyzed tandem aminofluorination of 1-phenyl-2-(4-phenylbut-3-yn-2-ylidene)hydrazine. Other

• 1/2 and comparison of 5 vs 6). The reaction conditions were compatible with a halogen substituent such as in 2e (Table 2, entries 7 and 8), which was obtained in up to 67% yield. Gratifyingly the presence of 4-substituted 1H-pyrazole allowed the clean formation of the corresponding difluoroadduct 2f

Continuous flow nitration in miniaturized devices

• Amol A. Kulkarni

Beilstein J. Org. Chem. 2014, 10, 405–424, doi:10.3762/bjoc.10.38

• by Panke et al. [27]. The nitration product of 1-methyl-3-propyl-1H-pyrazole-5-carboxylic acid is an intermediate for the “life-style drug” Sildenafil® (Scheme 1). Similarly, nitration of 2-methylindole, pyridine N-oxide and toluene (also with an acetyl nitrate Ac2O/HNO3 mixture) were conducted. The

• critical situation. It is important to note that the pyrazole was nitrated after dissolving it in the sulfuric acid. For a reactor of 10 mL volume, the temperature was maintained at 65 °C, and the hydrolysis was carried out by dropping the reaction mixture into a cold aqueous solution saturated with

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

Coupling of C-nitro-NH-azoles with arylboronic acids. A route to N-aryl-C-nitroazoles

• Marta K. Kurpet,
• Aleksandra Dąbrowska,
• Małgorzata M. Jarosz,
• Katarzyna Kajewska-Kania,
• Nikodem Kuźnik and
• Jerzy W. Suwiński

Beilstein J. Org. Chem. 2013, 9, 1517–1525, doi:10.3762/bjoc.9.173

• Materials, Polish Academy of Sciences, M. Curie-Skłodowskiej 34, Zabrze 41-819, Poland 10.3762/bjoc.9.173 Abstract A method for the synthesis of N-aryl-C-nitroazoles is presented. A coupling reaction between variously substituted arylboronic acids and 3(5)-nitro-1H-pyrazole catalyzed by copper salt has

• conditions on the yield of the product has been presented. Results and Discussion The group of products that we mainly describe is the 1-aryl derivatives of 3(5)-nitro-1H-pyrazole (1a). This is still a barely investigated group of compounds that can have attractive properties. Some recent reports describe

• ], and are described as being useful for the treatment of cognitive-deficit-associated psychiatric, neurodegenerative and neurological disorders [33]. Only four papers describe the synthesis of 3-nitro-1-phenyl-1H-pyrazole. It may be a product of oxidation of 3-amino-1-phenyl-1H-pyrazole [18], a product

Substituent effect on the energy barrier for σ-bond formation from π-single-bonded species, singlet 2,2-dialkoxycyclopentane-1,3-diyls

• Jianhuai Ye,
• Yoshihisa Fujiwara and
• Manabu Abe

Beilstein J. Org. Chem. 2013, 9, 925–933, doi:10.3762/bjoc.9.106

• method of Tiecco [32]. Pyrazole 3g was then synthesized by the reaction with hydrazine hydrate. AZg was obtained by the Diels–Alder [4 + 2]-cycloaddition with cyclopentadiene and hydrogenation using PtO2 as a catalyst. The endo-configured structure of azoalkanes AZc–g was determined by X-ray

• /z): [M + Na]+ calcd for C33H32O6N2Na, 575.21526; found, 575.21387; Rf = 0.27 (EtOAc/hexane = 30/70). 4,4-Dibenzyloxy-3,5-bis(3,5-dimethoxyphenyl)pyrazole (3e). Yellow powder (from MeOH), mp: 183–184 °C; IR (neat, cm−1): 3025, 2952, 2847, 1605, 1551, 1456, 1426, 1371, 1160, 1117, 849, 670; 1H NMR

• , phenyl), 130.47 (s, C, aryl), 136.24 (s, C, phenyl), 161.81 (s, COCH3), 167.53 (s, C); ESIMS (m/z): [M + H]+ calcd for C33H33N6O2, 553.23331; found, 553.23267; Rf = 0.13 (EtOAc/hexane = 20/80). 4,4-Bis(3,5-dimethoxybenzyloxy)-3,5-bis(3,5-dimethoxyphenyl)pyrazole (3f). IR (neat, cm−1): 3010, 2942, 1605

Dipyrazolo[1,5-a:4',3'-c]pyridines – a new heterocyclic system accessed via multicomponent reaction

• Wolfgang Holzer,
• Gytė Vilkauskaitė,
• Eglė Arbačiauskienė and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2012, 8, 2223–2229, doi:10.3762/bjoc.8.251

• multicomponent reaction affording new tricyclic compounds with a dipyrazolo[1,5-a:4',3'-c]pyridine core. Detailed NMR spectroscopic investigations (1H, 13C and 15N) were undertaken with all obtained compounds. Keywords: cyclization; nitrogen heterocycles; NMR spectroscopy; multicomponent reaction; pyrazole

• ; Introduction Condensed pyrazole scaffolds are important substructures of compounds with biological activity and can be found in some well-known drug molecules, such as, for example, Sildenafil (a pyrazolo[4,3-d]pyrimidine) [1][2], Allopurinol (a pyrazolo[3,4-d]pyrimidin-4-one) [3], Zaleplon (a pyrazolo[1,5-a

• novel condensed heterocyclic systems containing pyrazole substructures. Apart from a series of publications dealing with the construction of pyrazole analogues of xanthones and related systems [15][16][17][18][19][20] we recently described the synthesis of pyrano[4,3-c]pyrazol-4(1H)-ones and -4(2H)-ones

New efficient ligand for sub-mol % copper-catalyzed C–N cross-coupling reactions running under air

• Per-Fredrik Larsson,
• Peter Astvik and
• Per-Ola Norrby

Beilstein J. Org. Chem. 2012, 8, 1909–1915, doi:10.3762/bjoc.8.221

• (4) in moderate yield. To test the efficiency of DMDETA a kinetic study was performed by varying the concentration of the ligand and copper. As a standard reaction the copper-catalyzed cross coupling of pyrazole with iodobenzene was chosen (Scheme 2). The kinetic profile when varying the

• calcium hydride. Toluene was dried through distillation and stored under nitrogen. DMF was distilled over calcium hydride and stored under nitrogen. CuCl2 (Aldrich, purity of 99.999% metal basis), K3PO4 (98%), and pyrazole (98%) were stored under air- and moisture-free conditions. All other chemicals were

• to a maximum of 25% yield. The kinetic investigation was carried out by varying the concentration of one component and keeping the rest of the components constant under standard reaction conditions; pyrazole (136 mg, 2 mmol, 1 equiv), iodobenzene (334 μL, 1.5 equiv), CuCl2 (40 μL, 0.01 mol %) K3PO4

Synthesis and in silico screening of a library of β-carboline-containing compounds

• Kay M. Brummond,
• John R. Goodell,
• Matthew G. LaPorte,
• Lirong Wang and
• Xiang-Qun Xie

Beilstein J. Org. Chem. 2012, 8, 1048–1058, doi:10.3762/bjoc.8.117

• pyrazole group of 6{10}. Ligand-based strategy for target prediction Ligand-based target prediction algorithms have been developed based upon an established medicinal chemistry principle that structurally similar compounds, with comparable physical properties, should convey related biological properties

Fluorescent hexaaryl- and hexa-heteroaryl[3]radialenes: Synthesis, structures, and properties

• Antonio Avellaneda,
• Courtney A. Hollis,
• Xin He and
• Christopher J. Sumby

Beilstein J. Org. Chem. 2012, 8, 71–80, doi:10.3762/bjoc.8.7

• deficient hexaaryl[3]radialene observed thus far, and studies of their electrochemical and photophysical properties. Results and Discussion The first new [3]radialene compound targeted was hexa(pyrazol-1-yl)[3]radialene. However, the required starting material, 1-[(1H-pyrazol-1-yl)methyl]-1H-pyrazole

• considerable upfield shifts of the pyrazole H4 proton (5.69 ppm) and the methyl hydrogen atoms (1.80 and 2.07 ppm) arising from the double-bladed propeller conformation adopted by 1. In addition to the study of [3]radialenes with heterocyclic donors [18][19], we have devoted substantial attention to the study

Regioselectivity in the multicomponent reaction of 5-aminopyrazoles, cyclic 1,3-diketones and dimethylformamide dimethylacetal under controlled microwave heating

• Kamal Usef Sadek,
• Ramadan Ahmed Mekheimer,
• Tahany Mahmoud Mohamed,
• Moustafa Sherief Moustafa and
• Mohamed Hilmy Elnagdi

Beilstein J. Org. Chem. 2012, 8, 18–24, doi:10.3762/bjoc.8.3

• triethylamine as base produces the more thermodynamically stable dihydropyridine (Hantzsch-type product). In addition, the nature of the catalyst plays an important role [20]. A one-pot three component reaction of 5-amino-1H-pyrazole-4-carbonitrile, dimedone and triethylorthoesters in toluene under reflux was

• -3-methyl-pyrazole, aromatic aldehydes and dimedone under controlled microwave irradiation at 150 °C involves the participation of C3-H of the pyrazole ring in such a cyclocondensation reaction, this is not favoured in our case. In addition two signals were assigned to two CH2 groups and three methyl

• recrystallized from EtOH to give a pure sample of 8 as orange crystals, 303 mg (88% yield); mp 255–256 °C; 1H NMR (400 MHz, DMSO-d6) δ 1.01 (s, 6H, 2 CH3), 2.40 (s, 2H, CH2), 3.26 (s, 2H, CH2), 7.24–7.85 (m, 6H, 5 Ph-H and CH-NH), 11.76 (s, 1H, NH), 12.59 (s, 1H, pyrazole NH); 13C NMR (100 MHz, DMSO-d6) δ 27.95

(How) does 1,3,5-triethylbenzene scaffolding work? Analyzing the abilities of 1,3,5-triethylbenzene- and 1,3,5-trimethylbenzene-based scaffolds to preorganize the binding elements of supramolecular hosts and to improve binding of targets

• Xing Wang and
• Fraser Hof

Beilstein J. Org. Chem. 2012, 8, 1–10, doi:10.3762/bjoc.8.1

• conformer, namely uddudd. One can expect a significant effect of the nature of the recognition elements on conformational energies. Many recognition elements that vary in shape, functionality, charge, and chirality have been reported. We picked pyrazole-derived hosts 4 (used for cation binding) [17] and

• ) charge–charge repulsion in the gas-phase calculations on 5Et. The calculated results of pyrazole-substituted 4Et are quite similar in the gas phase and water. On comparison of the results of 4Et to hexaethylbenzene, it is seen that the sequential ordering of the conformational energies is the same. But

• the ududud conformer of pyrazole-substituted 4Et is only 2.9 kcal/mol more stable than the second-lowest-energy conformation in water, a gap that is a significant 1.4 kcal/mol smaller than the value calculated for hexaethylbenzene (4.3 kcal/mol). We interpret this difference in terms of the steric

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

• ]isoindole (11, 12.5% yield) and trans-3-(4-methylphenyl)-3a,8-dihydro-3H-pyrazolo[5,1-a]isoindole (12, 5% yield). Thermal reactions afforded 3-(4-methylphenyl)-3,3a,8,8a-tetrahydroindeno[2,1-c]pyrazole (14, 50% yield) and 11-(4-methylphenyl)-9,10-diazatricyclo[7.2.1.02,7]dodeca-2,4,6,10-tetraene (15, 22

• ] 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

Efficient synthesis of 1,3-diaryl-4-halo-1H-pyrazoles from 3-arylsydnones and 2-aryl-1,1-dihalo-1-alkenes

• Yiwen Yang,
• Chunxiang Kuang,
• Hui Jin,
• Qing Yang and
• Zhongkui Zhang

Beilstein J. Org. Chem. 2011, 7, 1656–1662, doi:10.3762/bjoc.7.195

• moderate to excellent yields. 1,3-Diaryl-4-halo-1H-pyrazoles are found to be important intermediates that can easily be converted into 1,2,5-triaryl-substituted pyrazoles via Pd-catalyzed C–H bond activation. Keywords: C–H bond activation; cycloaddition; dihaloalkenes; pyrazole; sydnones; Introduction

• Over the past decade, pyrazoles as key motifs in biologically active compounds have received increasing attention from the synthetic community. Diazoles can be employed as a central building block in the synthesis of compound libraries in the pharmaceutical [1] and agrochemical [2] industries. Pyrazole

• [9] and fungicides [10], and as well as antiviral [11] and antibacterial agents [12]. Pyrazoles are gaining interest as ligands for transition metals, and in the field of materials chemistry [13][14]. Pyrazole and its derivatives can be synthesized by several methods [15]. The most common approach is

Synthesis and oxidation of some azole-containing thioethers

• Andrei S. Potapov,
• Nina P. Chernova,
• Vladimir D. Ogorodnikov,
• Tatiana V. Petrenko and
• Andrei I. Khlebnikov

Beilstein J. Org. Chem. 2011, 7, 1526–1532, doi:10.3762/bjoc.7.179

• Akademicheskii Ave., 634055 Tomsk, Russia 10.3762/bjoc.7.179 Abstract Pyrazole and benzotriazole-containing thioethers, namely 1,5-bis(3,5-dimethylpyrazol-1-yl)-3-thiapentane, 1,8-bis(3,5-dimethylpyrazol-1-yl)-3,6-dithiaoctane and 1,3-bis(1,2,3-benzotriazol-1-yl)-2-thiapropane were prepared and fully

• characterized. Oxidation of the pyrazole-containing thioether by hydrogen peroxide proceeds selectively to provide a sulfoxide or sulfone, depending on the amount of oxidant used. Oxidation of the benzotriazole derivative by hydrogen peroxide is not selective, and sulfoxide and sulfone form concurrently

• . Selenium dioxide-catalyzed oxidation of benzotriazole thioether by H2O2, however, proceeds selectively and yields sulfoxide only. Keywords: azole; oxidation; sulfone; sulfoxide; thioether; Introduction Compounds comprising two pyrazole moieties linked by an aliphatic spacer act as bidentate chelating

Amines as key building blocks in Pd-assisted multicomponent processes

• Didier Bouyssi,
• Nuno Monteiro and
• Geneviève Balme

Beilstein J. Org. Chem. 2011, 7, 1387–1406, doi:10.3762/bjoc.7.163

• different approach to α,β-alkynyl ketone derivatives as pyrazole precursors. They established a four-component domino process combining various organic halides, terminal alkynes, hydrazines, and carbon monoxide at room temperature. In this case, all components are mixed at the very beginning of the process

• are formed, they immediately react with hydrazine to form pyrazole by a specific rate acceleration in the one-pot process [16]. The Sonogashira cross-coupling of acid chlorides with terminal alkynes has also been demonstrated as a valuable tool to generate, in situ, ynones bearing a pendant amine

• . Synthesis of masked 3-aminoindan-1-ones. Synthesis of homoallylic amines and α-aminoesters. Preparation of 1,2-dihydroisoquinolin-1-ylphosphonates. Pyrazole elaboration by cycloaddition of hydrazines with alkynones generated in situ. An alternative approach to pyrazoles involving hydrazine cycloaddition

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

• chloride. Considering our interest in IMCR, we envisioned that a similar cascade could be performed on a properly functionalized Ugi adduct allowing us to reach a new 4-component access to pyrazole derivatives. The present letter summarizes our efforts in this direction. Results and Discussion Among the

Continuous gas/liquid–liquid/liquid flow synthesis of 4-fluoropyrazole derivatives by selective direct fluorination

• Jessica R. Breen,
• Graham Sandford,
• Dmitrii S. Yufit,
• Judith A. K. Howard,
• Jonathan Fray and
• Bhairavi Patel

Beilstein J. Org. Chem. 2011, 7, 1048–1054, doi:10.3762/bjoc.7.120

• pyrazole derivatives [22][23]. Of relevance to this paper, pyrazole and its derivatives constitute an important class of compounds, which exhibit various biological and pharmaceutical activities ranging from antitumor to anti-inflammatory, antipsychotic, antimicrobial, antiviral and antifungal activities

• pyrazole substrates using elemental fluorine and, in many cases, obtained low yields of the desired fluoropyrazole products due to significant tar formation [24], while the corresponding fluorination of a limited number of pyrazole systems by SelectfluorTM has been described by other researchers [25

• conditions that would convert all of the diketone substrate to a fluorodiketone in the first stage of the continuous process. Subsequent separation of fluoropyrazole (4a) from the corresponding non-fluorinated pyrazole, formed by the coupling of not reacted pentane-2,4-dione and hydrazine, was difficult to

An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals

• Marcus Baumann,
• Ian R. Baxendale,
• Steven V. Ley and
• Nikzad Nikbin

Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57

• , after chromatography, the bicyclic structure in good overall isolated yield (Scheme 46). Despite this synthesis being much shorter and convergent it has some limitations since the entire procedure needs to be performed in a glove box and has consequently only been reported on small scale. Pyrazole

• moiety and the trifluoromethylated pyrazole core with its negative electrostatic potential play a key role in apoptosis induction. Consequently, the anti-inflammatory and apoptosis inducing properties of celecoxib are assumed to result via different modes of action. In a recent study [71], celecoxib has

• 236 and the substituted hydrazine 237 [72][73] (Scheme 47). The immediate downside to this approach is the generation of regioisomeric mixtures. However, this is often of minor concern. In the commercial process only 2–5% of the unwanted regioisomer is produced, with the purified pyrazole being