Unprecedented synthesis of a 14-membered hexaazamacrocycle

• Anastasia A. Fesenko and
• Anatoly D. Shutalev

Beilstein J. Org. Chem. 2023, 19, 1728–1740, doi:10.3762/bjoc.19.126

• Anastasia A. Fesenko Anatoly D. Shutalev N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky Ave., 119991 Moscow, Russian Federation 10.3762/bjoc.19.126 Abstract The transformation of 3-[(ethoxymethylene)amino]-1-methyl-1H-pyrazole-4-carbonitrile into the 14

• -2-methyl-2,4-dihydro-5H-pyrazolo[3,4-d]pyrimidin-5-amine described by Baraldi et al. [41] using the reaction of 3-[(ethoxymethylene)amino]-1-methyl-1H-pyrazole-4-carbonitrile with excess hydrazine hydrate in EtOH under reflux. However, a pyrazole-fused 1,2,4,8,9,11-hexaazamacrocycle was unexpectedly

• the detailed studies of the hydrazine-promoted transformation of 3-[(ethoxymethylene)amino]-1-methyl-1H-pyrazole-4-carbonitrile (4) or 4-imino-2-methyl-2,4-dihydro-5H-pyrazolo[3,4-d]pyrimidin-5-amine (8) into 2,10-dimethyl-2,8,10,16-tetrahydrodipyrazolo[3,4-e:3',4'-l][1,2,4,8,9,11

An efficient metal-free and catalyst-free C–S/C–O bond-formation strategy: synthesis of pyrazole-conjugated thioamides and amides

• Shubham Sharma,
• Dharmender Singh,
• Sunit Kumar,
• Vaishali,
• Rahul Jamra,
• Naveen Banyal,
• Deepika,
• Chandi C. Malakar and
• Virender Singh

Beilstein J. Org. Chem. 2023, 19, 231–244, doi:10.3762/bjoc.19.22

• -tethered thioamides inspired us to generate analogous pyrazole-pyridine conjugates having an amide linkage. For this purpose, 5-(4-fluorophenyl)-1-phenyl-1H-pyrazole-3-carbaldehyde (1) and 2-aminopyridine (F) were selected as the model reactants to explore this transformation. Initially, we conducted an

• product was the desired product, 5-(4-fluorophenyl)-1-phenyl-N-(pyridin-2-yl)-1H-pyrazole-3-carboxamide (1F), as analyzed by spectroscopic data. Next, we screened other organic solvents including DMF, CH3CN, THF, and MeOH to improve the yield of the desired product 1F, but only a slight improvement in the

• . Using this method, 3-(4-chlorophenyl)-1-phenyl-N-(pyridin-2-yl)-1H-pyrazole-5-carboxamide (10F) was produced in good yield (62%), while 9F was generated in low yield (36%) as depicted in Scheme 8. Based on the current experimental observations and literature reports [62][83] a plausible mechanistic

Chemistry of polyhalogenated nitrobutadienes, 17: Efficient synthesis of persubstituted chloroquinolinyl-1H-pyrazoles and evaluation of their antimalarial, anti-SARS-CoV-2, antibacterial, and cytotoxic activities

• Viktor A. Zapol’skii,
• Isabell Berneburg,
• Ursula Bilitewski,
• Melissa Dillenberger,
• Katja Becker,
• Stefan Jungwirth,
• Aditya Shekhar,
• Bastian Krueger and
• Dieter E. Kaufmann

Beilstein J. Org. Chem. 2022, 18, 524–532, doi:10.3762/bjoc.18.54

• Plasmodium has been developed and is reported in the literature [24]. Results and Discussion The vinylic SN reaction of 2-nitroperchlorobutadiene (1) with four equivalents of the azoles such as 1H-pyrazole, 1H-1,2,4-triazole, or 1H-benzotriazole affords similarly to [25] the corresponding 1,1

• -Elimination of an azole from A leads to formation of an isolable diene B. Upon further heating, the amino group attacks the electrophilic C–Cl position of the trichlorovinylic group intramolecularly, leading to a 2,3-dihydro-1H-pyrazole C. Finally, pyrazoles 3 are obtained upon 1,3-elimination of hydrochloric

Regioselective synthesis of methyl 5-(N-Boc-cycloaminyl)-1,2-oxazole-4-carboxylates as new amino acid-like building blocks

• Jolita Bruzgulienė,
• Greta Račkauskienė,
• Aurimas Bieliauskas,
• Vaida Milišiūnaitė,
• Miglė Dagilienė,
• Gita Matulevičiūtė,
• Vytas Martynaitis,
• Sonata Krikštolaitytė,
• Frank A. Sløk and
• Algirdas Šačkus

Beilstein J. Org. Chem. 2022, 18, 102–109, doi:10.3762/bjoc.18.11

• peptide-like structure. Heterocyclic amino acids and related compounds have been used to prepare synthetic DNA-encoded compound libraries for the discovery of small molecule protein ligands [23][24][25]. Recently, a highly specific and potent p38α kinase inhibitor containing a 3-amino-1-phenyl-1H-pyrazole

Synthesis of new pyrazolo[1,2,3]triazines by cyclative cleavage of pyrazolyltriazenes

• Nicolai Wippert,
• Martin Nieger,
• Claudine Herlan,
• Nicole Jung and
• Stefan Bräse

Beilstein J. Org. Chem. 2021, 17, 2773–2780, doi:10.3762/bjoc.17.187

• synthetically and successful syntheses of different manifold isomers. 3,6-Dihydro-4H-pyrazolo[3,4-d][1,2,3]triazin-4-ones 2, as one example of the diverse compound class, can be gained via diazotization of 3-amino-1H-pyrazole-4-carboxamides 1a or 3-amino-1H-pyrazole-4-carbonitriles 1b and subsequent cyclization

• the starting 3-amino-1H-pyrazole-4-carboxamides 1a or 3-amino-1H-pyrazole-4-carbonitriles 1b is altered [26]. Furthermore, several 2,7-dihydro-3H-imidazo[1,2-c]pyrazolo[4,3-e][1,2,3]triazines 4 were described. However, while 3,6-substituted-3,6-dihydro-4H-pyrazolo[3,4-d][1,2,3]triazin-4-ones 2 and 3,7

• the designed synthetic route, 3-(3,3-diisopropyltriaz-1-en-1-yl)-1H-pyrazole-4-carbonitrile (15) was synthesized in a first step using the commercially available 3-amino-1H-pyrazole-4-carbonitrile (16). Thus, the aminopyrazole was diazotized in aqueous media using hydrochloric acid and sodium nitrite

Copper-mediated oxidative C−H/N−H activations with alkynes by removable hydrazides

• Feng Xiong,
• Bo Li,
• Chenrui Yang,
• Liang Zou,
• Wenbo Ma,
• Linghui Gu,
• Ruhuai Mei and
• Lutz Ackermann

Beilstein J. Org. Chem. 2021, 17, 1591–1599, doi:10.3762/bjoc.17.113

• context, You [25], Huang [26], Liu [27], Li [28], and co-workers elegantly disclosed copper-mediated/catalyzed cascade C−H alkynylation and annulation with terminal alkynes to afford 3-methyleneisoindolinone derivatives, through the assistance of 8-aminoquinoline [29] or 2-aminophenyl-1H-pyrazole [30

Synthesis of trifluoromethyl ketones by nucleophilic trifluoromethylation of esters under a fluoroform/KHMDS/triglyme system

• Yamato Fujihira,
• Yumeng Liang,
• Makoto Ono,
• Kazuki Hirano,
• Takumi Kagawa and
• Norio Shibata

Beilstein J. Org. Chem. 2021, 17, 431–438, doi:10.3762/bjoc.17.39

• common nitrogen-containing compounds such as pyridine, pyrazine, 1H-pyrazole, 1H-indole, 1-methyl-1H-indole, piperidine, and piperazine were subjected to screening. Pyridine and piperidine slightly hamper the reaction of 1g (Table 2, entries 2 and 7, 80–82%). Other nitrogen-containing compounds have more

Access to highly substituted oxazoles by the reaction of α-azidochalcone with potassium thiocyanate

• Mysore Bhyrappa Harisha,
• Pandi Dhanalakshmi,
• Rajendran Suresh,
• Raju Ranjith Kumar and
• Shanmugam Muthusubramanian

Beilstein J. Org. Chem. 2020, 16, 2108–2118, doi:10.3762/bjoc.16.178

• synthesis of 2,4,5-trisubstituted oxazole from azirine. a) I2, PPh3; b) NaH, 1H-pyrazole; c) 2-bromoacetyl bromide, NaN3; d) heating; e) t-BuOK; f) Ph-CHO, visible light; g) KSCN, K2S2O8. Scope of the α-azidochalcones. The reactions were carried out at reflux temperature, using 1 (1 mmol), 2 (3 mmol

Anthelmintic drug discovery: target identification, screening methods and the role of open science

• Frederick A. Partridge,
• Ruth Forman,
• Carole J. R. Bataille,
• Graham M. Wynne,
• Marina Nick,
• Angela J. Russell,
• Kathryn J. Else and
• David B. Sattelle

Beilstein J. Org. Chem. 2020, 16, 1203–1224, doi:10.3762/bjoc.16.105

• on to demonstrate that 24 showed a broad activity against other nematode parasite models: H. polygyrus, A. ceylanicum and T. muris. A broadly-related 1-methyl-1H-pyrazole-5-carboxamide series has also been investigated in detail, with compounds identified that show substantially improved potency and

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

• Yana I. Sakhno,
• Maryna V. Murlykina,
• Oleksandr I. Zbruyev,
• Anton V. Kozyryev,
• Svetlana V. Shishkina,
• Dmytro Sysoiev,
• Vladimir I. Musatov,
• Sergey M. Desenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2020, 16, 281–289, doi:10.3762/bjoc.16.27

• Republic 10.3762/bjoc.16.27 Abstract Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of

• 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines. Keywords: 5-amino-1H-pyrazole-4-carbonitrile; 3-amino-1,2,4-triazole; 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines; heterocycle; multicomponent reaction; ultrasonication; Introduction Tetrahydropyrimidines are heterocycles of high pharmacological

• reactions involving pyruvic acids (pyruvates) and different α-aminoazoles. Synthesis of 4-arylamino-substituted tetrahydroquinolines. Ultrasound-assisted multicomponent reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile, aldehydes, and pyruvic acid/ethyl pyruvate. Synthesis of 3-cyano

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors

• Man-Man Wang,
• Hao Huang,
• Lei Shu,
• Jian-Min Liu,
• Jian-Qiu Zhang,
• Yi-Le Yan and
• Da-Yong Zhang

Beilstein J. Org. Chem. 2020, 16, 233–247, doi:10.3762/bjoc.16.25

• substituted 1,3-dimethyl-1H-pyrazole-5-ol, using DMAP as the catalyst. Subsequently, the key enol ester E and M were respectively obtained. Finally, Fries-type rearrangements were performed in anhydrous DCM at room temperature to afford the title compounds I and III [31]. As shown in Scheme 4, the title

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

One-pot activation–alkynylation–cyclization synthesis of 1,5-diacyl-5-hydroxypyrazolines in a consecutive three-component fashion

• Christina Görgen,
• Katharina Boden,
• Guido J. Reiss,
• Walter Frank and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 1360–1370, doi:10.3762/bjoc.15.136

• , starting from phenylglyoxylic acid (1a), phenylacetylene (2a), and Boc-hydrazide (4a) through the formation of 1,4-diphenylbut-3-yne-1,2-dione (3a), with subsequent N-deacylation as the consequence of basic work-up (Scheme 2), furnished 5-benzoyl-3-phenyl-1H-pyrazole (6a) in 41% isolated yield. In addition

• or Brønsted acidic conditions were accompanied by simultaneous deacylation of substituent R3 finally furnishing 5-(hetero)aroyl-3-(hetero)aryl-1H-pyrazole 6a (for attempted dehydrative aromatization, see Supporting Information File 1, Table S5), as already reported for alkaline deprotection

• ) and antibacterial activity (center and right). ORTEP plot of 5-benzoyl-3-phenyl-1H-pyrazole (6a) (thermal ellipsoids at 30% probability); the direction of intermolecular N−H···O hydrogen bonding is indicated by dashed lines. Ellipsoid plot of 1-Boc-5-benzoyl-5-hydroxypyrazoline 5a. ORTEP plot and

Molecular iodine-catalyzed one-pot multicomponent synthesis of 5-amino-4-(arylselanyl)-1H-pyrazoles

• Camila S. Pires,
• Daniela H. de Oliveira,
• Maria R. B. Pontel,
• Jean C. Kazmierczak,
• Roberta Cargnelutti,
• Diego Alves,
• Raquel G. Jacob and
• Ricardo F. Schumacher

Beilstein J. Org. Chem. 2018, 14, 2789–2798, doi:10.3762/bjoc.14.256

• -(phenylselanyl)-1H-pyrazol-5-amine was submitted to an oxidative dehydrogenative coupling to produce a diazo compound confirmed by X-ray analysis. Keywords: diaryl diselenide; diazo compound; 1H-pyrazole; molecular iodine; multicomponent reaction; Introduction Selenium-containing compounds are of great

• the 3-methyl-5-methylsulfanyl-4-phenylselanyl-1H-pyrazole [10]. Our research group described the multicomponent synthesis of 3,5-dimethyl-4-arylselanyl-1H-pyrazoles catalyzed by copper iodide using DMSO as solvent [4]. More recently, Zora and co-workers reported the one-pot preparation of 4

• diselenides were efficiently coupled to 5-amino-1H-pyrazole to produce the corresponding products in yields ranging from 24% to 80%. However, when the bulkier 1,2-dimesityl diselenide 3f was employed, no product was obtained (Table 2, entry 16). To gain insight into the mechanistic profile we also evaluated

[3 + 2]-Cycloaddition reaction of sydnones with alkynes

• Veronika Hladíková,
• Jiří Váňa and
• Jiří Hanusek

Beilstein J. Org. Chem. 2018, 14, 1317–1348, doi:10.3762/bjoc.14.113

• -diphenyl-1H-pyrazole. The calculated difference in energies of transition states leading to 1,3- and 1,4-diphenyl-1H-pyrazole (4.1 kcal·mol−1 = 17.2 kJ·mol−1) predicts at 140 °C the ratio ≈99:1 which corresponds well with found experimental value >95:5 (see entry 3 in Table 4 [83]). There are only some

Sequential Ugi reaction/base-induced ring closing/IAAC protocol toward triazolobenzodiazepine-fused diketopiperazines and hydantoins

• Robby Vroemans,
• Fante Bamba,
• Jonas Winters,
• Joice Thomas,
• Jeroen Jacobs,
• Luc Van Meervelt,
• Jubi John and
• Wim Dehaen

Beilstein J. Org. Chem. 2018, 14, 626–633, doi:10.3762/bjoc.14.49

• inseparable mixture of diastereomers. Various attempts were made with other azidobenzaldehydes (5-azido-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde, 2-azidoquinoline-3-carbaldehyde and 2-azido-5-nitrobenzaldehyde) and isocyanides (2-morpholinoethyl isocyanide) towards the synthesis of diketopiperazine-fused

• -methyl-1-phenyl-1H-pyrazole-4-carbaldehyde). The success in the synthesis of diketopiperazine-fused triazolobenzodiazepine prompted us to examine the possibility of making the sequential synthetic route in ‘one-pot’ starting from the Ugi 4-CR (Scheme 4). Thus we initiated the reaction sequence from the

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• described the construction of spiro[indoline-3,4'-pyrazolo[3,4-b]pyridine] derivatives 57 from the multicomponent reaction of 5-amino-3-hydroxy-1-phenyl-1H-pyrazole (46), ketones 56 and isatin 54 in water/acetic acid (3:1) at 90 °C (Scheme 12). Quiroga et al. [58] reported the synthesis of the pyrazolo[3,4

• products in small amounts namely 3(5)-methyl-5(3)-phenyl-1H-pyrazole (121) obtained by CN bond cleavage and benzoic acid (122) was also observed (Scheme 33). The structure of the regioisomer was established unequivocally by performing 1H,13C-HMQC, 1H,13C- and 1H,15N-HMBC experiments. Aqueous mediated

• 200 from the cyclocondensation of 5-amino-1-(2,4-dinitrophenyl)-1H-pyrazole-4-carboxamide (199) with aromatic aldehydes in the presence of iodine in acetonitrile (Scheme 55). The synthesized pyrazolo[3,4-d]pyrimidines were evaluated for antibacterial activities. Venkatesan et al. [132] also used 4

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• efficient and regioselective synthesis of pyrazolo[1,5-a]pyrimidines and aryl[heteroaryl]pyrazolo[1,5-a]pyrimidines in acetic acid under reflux. The regioselectivity was attributed to the high nucleophilicity of the amino group in 3-amino-5-methyl-1H-pyrazole and the high electrophilicity of the β-carbon

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• corresponding 1H-pyrazole 36. The cycloaddition occurred with preservation of the configuration of the dipolarophile. In the presence of excess diazomethane the five-membered cycloadducts 35 and 36 were converted into a complex mixture of products. In a very recent study, we demonstrated that the reactions of

• . Stepwise [3 + 2]-cycloadditions of dimethyl dicyanofumarate (E-1b) and dimethyl dicyanomaleate (Z-1b) with the in situ generated azomethine ylides 32. [3 + 2]-Cycloaddition of diazomethane with dimethyl dicyanofumarate (E-1b) leading to 1H-pyrazole derivative 36. Reversible Diels–Alder reaction of fulvenes

New tricks of well-known aminoazoles in isocyanide-based multicomponent reactions and antibacterial activity of the compounds synthesized

• Maryna V. Murlykina,
• Maryna N. Kornet,
• Sergey M. Desenko,
• Svetlana V. Shishkina,
• Oleg V. Shishkin,
• Aleksander A. Brazhko,
• Vladimir I. Musatov,
• Erik V. Van der Eycken and
• Valentin A. Chebanov

Beilstein J. Org. Chem. 2017, 13, 1050–1063, doi:10.3762/bjoc.13.104

• , Zhukovsky str., 66, 69600, Zaporizhzhya, Ukraine Faculty of Chemistry, V. N. Karazin Kharkiv National University, Svobody sq., 4, 61077, Kharkiv, Ukraine 10.3762/bjoc.13.104 Abstract The well-known aminoazoles, 3-amino-5-methylisoxazole and 5-amino-N-aryl-1H-pyrazole-4-carboxamides, were studied as an

• -aryl-1H-pyrazole-4-carboxamides; antibacterial activity; Groebke–Blackburn–Bienaymé reaction; isocyanide Ugi reaction; Introduction An intensive progress in pharmaceutical and medicinal chemistry, as well as in the generation and improvement of medicinal technologies has led to defeating a wide scope

• sometimes similar to 3-amino-1,2,4-triazole that was described as a component of GBB-3CR earlier [71][72][73][74][75]. Therefore, the first type of aminoazoles studied in our work was 5-amino-N-aryl-1H-pyrazole-4-carboxamide that showed 1,3-binucleophile properties in the condensation with aromatic

p-Nitrophenyl carbonate promoted ring-opening reactions of DBU and DBN affording lactam carbamates

• Madhuri Vangala and
• Ganesh P Shinde

Beilstein J. Org. Chem. 2016, 12, 2086–2092, doi:10.3762/bjoc.12.197

• nucleophiles towards halo derivatives of main group elements where the DBU and DBN bicyclic rings remained unaffected [10][11]. Later in 1994, Lammers et al. observed the nucleophilicity of amidine bases with 4-halo-3,5-dimethyl-1-nitro-1H-pyrazole and their subsequent ring opening leading to the lactam

Catalytic Chan–Lam coupling using a ‘tube-in-tube’ reactor to deliver molecular oxygen as an oxidant

• Carl J. Mallia,
• Paul M. Burton,
• Alexander M. R. Smith,
• Gary C. Walter and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2016, 12, 1598–1607, doi:10.3762/bjoc.12.156

• -phenyl-1H-pyrazole (18) as the nucleophile with a number of different phenylboronic acids gave moderate to good yields (38–82% yields). In general electron-rich phenylboronic acids (19, 29–32, Scheme 2) gave better yields than electron poor ones (33–35, Scheme 2). This is probably due to the more

• -rich (65% yield) and electron-poor (38% yield) 2-substituted phenylboronic acids, most likely due to steric factors (31 and 35, Scheme 2). It is noteworthy that for all of the 3-phenyl-1H-pyrazole couplings, only the 1,3-disubsituted pyrazole products were obtained with no 1,5-disubsituted isomers

A convenient four-component one-pot strategy toward the synthesis of pyrazolo[3,4-d]pyrimidines

• Mingxing Liu,
• Jiarong Li,
• Hongxin Chai,
• Kai Zhang,
• Deli Yang,
• Qi Zhang and
• Daxin Shi

Beilstein J. Org. Chem. 2015, 11, 2125–2131, doi:10.3762/bjoc.11.229

• -phenyl-1H-pyrazole-4-carbonitrile (6a) with benzaldehyde and ethanol, the cyclization of (E)-5-(benzylideneamino)-1-phenyl-1H-pyrazole-4-carbonitrile (7a) with ethanol or the reaction of 1,6-diphenyl-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one (5aa) with ethanol, respectively (Scheme 2). With those

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

•  23). Shortly after, the Lu group further expanded the substrate scope of asymmetric [3 + 2] annulations with allenoates to a series of 3,5-dimethyl-1H-pyrazole-derived acrylamides (Scheme 24) [55]. The dipeptide-based phosphine H10 effectively promoted the reaction in good to excellent yields, albeit

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 precursor. Employing the latter approach we recently presented a novel method for the synthesis of the pyrazolo[4,3-c]pyridine system by Sonogashira-type cross-coupling reaction of easily obtainable 5-chloro-1-phenyl-1H-pyrazole-4-carbaldehydes with various alkynes and subsequent ring-closure

• reaction of the thus obtained 5-alkynyl-1H-pyrazole-4-carbaldehydes in the presence of tert-butylamine [17]. Furthermore, we showed that the oximes derived from the before mentioned 5-alkynylpyrazole-4-carbaldehydes can be transformed into the corresponding 1-phenylpyrazolo[4,3-c]pyridine 5-oxides [17