Formaldehyde surrogates in multicomponent reactions

• Cecilia I. Attorresi,
• Javier A. Ramírez and
• Bernhard Westermann

Beilstein J. Org. Chem. 2025, 21, 564–595, doi:10.3762/bjoc.21.45

• catalyst. Another recent example for the use of DMSO as C1 synthon was reported by Bhattacharjee et al. They used DMSO in a 3CR to install a methylene unit between an indazole 24 and a carboxylic acid 25 (Scheme 18) [52]. Under radical conditions using K2S2O8, they obtained a series of carboxylic acid

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

• the n + 1 MOs of the carborane prevents significant electronic delocalization between the two fused components. This contrasts with the fusion of pyrazole and benzene to form indazole, where both rings maintain their 2D aromaticity. Our findings demonstrate that the peripheral σ-aromaticity of

• 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

• of the N–N bond in pyrazole might help preserve its aromaticity. To explore this, we performed quantum chemical analyses on a range of o-carborane-fused pyrazoles and pyrazolines and compared them with their fully planar indazole and indazoline analogues. Aromaticity or non-aromaticity can be

Dioxazolones as electrophilic amide sources in copper-catalyzed and -mediated transformations

• Seungmin Lee,
• Minsuk Kim,
• Hyewon Han and
• Jongwoo Son

Beilstein J. Org. Chem. 2025, 21, 200–216, doi:10.3762/bjoc.21.12

• motifs such as a benzofuran, indazole, and quinoline were also shown to undergo the desired Markovnikov amidation with high efficiency (23j–l). Several mechanistic experiments were performed to rationalize the reaction pathways. As shown in Figure 7, copper hydride, generated from a copper precatalyst

Regioselective alkylation of a versatile indazole: Electrophile scope and mechanistic insights from density functional theory calculations

• Pengcheng Lu,
• Luis Juarez,
• Paul A. Wiget,
• Weihe Zhang,
• Krishnan Raman and
• Pravin L. Kotian

Beilstein J. Org. Chem. 2024, 20, 1940–1954, doi:10.3762/bjoc.20.170

• Structural Biology, BioCryst Pharmaceuticals Inc., Discovery Center of Excellence, 2100 Riverchase Center Building 200, Suite 200 Birmingham, AL, 35244, USA 10.3762/bjoc.20.170 Abstract Herein, we report a pair of regioselective N1- and N2-alkylations of a versatile indazole, methyl 5-bromo-1H-indazole-3

• other non-covalent interactions (NCIs) drive the N2-product formation. Methyl 1H-indazole-7-carboxylate (18) and 1H-indazole-3-carbonitrile (21) were also subjected to the reaction conditions and their mechanisms were evaluated. The N1- and N2-partial charges and Fukui indices were calculated for

• compounds 6, 18, and 21 via natural bond orbital (NBO) analyses which further support the suggested reaction pathways. Keywords: DFT; indazole; indazole substitution; mechanism; N1-substituted indazole; N2-substituted indazole; regioselectivity; Introduction Indazoles constitute an important class of

Three-component N-alkenylation of azoles with alkynes and iodine(III) electrophile: synthesis of multisubstituted N-vinylazoles

• Jun Kikuchi,
• Roi Nakajima and
• Naohiko Yoshikai

Beilstein J. Org. Chem. 2024, 20, 891–897, doi:10.3762/bjoc.20.79

• between various azoles and internal alkynes is mediated by benziodoxole triflate as the electrophile in a trans-fashion, affording azole-bearing vinylbenziodoxoles in moderate to good yields. The tolerable azole nuclei include pyrazole, indazole, 1,2,3-triazole, benzotriazole, and tetrazole. The iodanyl

• catalysis encompassed various azoles such as pyrazole, indazole, and (benzo)triazole, exhibiting high Z-selectivity. In addition, Cao et al. reported a gold-catalyzed addition of 5-substituted tetrazoles to terminal alkynes [11]. Analogous hydroazolation reactions of alkynes have also been achieved under

• reaction of azoles with alkynes and iodine(III) electrophile, benziodoxole triflate (BXT, 1; Scheme 1c). Displaying exclusive trans-selectivity, the reaction tolerates a broad range of azoles, including pyrazole, 1,2,3-triazole, tetrazole, indazole, and benzotriazole, with internal alkynes as coupling

N-Boc-α-diazo glutarimide as efficient reagent for assembling N-heterocycle-glutarimide diads via Rh(II)-catalyzed N–H insertion reaction

• Grigory Kantin,
• Pavel Golubev,
• Alexander Sapegin,
• Alexander Bunev and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2023, 19, 1841–1848, doi:10.3762/bjoc.19.136

• pyrazole derivatives (including indazole), benzimidazole, 1,2,3-triazole, indole, carbazole, indoline, quinazoline, and isoquinoline. Nevertheless, many heterocyclic motifs still remain beyond the attention of researchers. For example, glutarimides that incorporate tetrazole and 1,2,4-triazole substituents

• reaction with indazole, compound 6g, formed as a result of the attack of the carbenoid on the 2-N atom, was obtained. The regioselectivity of the reaction with 7-azaindazole was similar, however, the introduction of an additional basic nitrogen atom resulted in a significant increase in reaction time and a

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

Synthesis and reactivity of azole-based iodazinium salts

• Thomas J. Kuczmera,
• Annalena Dietz,
• Andreas Boelke and
• Boris J. Nachtsheim

Beilstein J. Org. Chem. 2023, 19, 317–324, doi:10.3762/bjoc.19.27

• % yields. In the latter case, the initially generated hydroxy-iodonium salt is stabilized via the indazole nitrogen [26] and the steric hindrance by the methyl group is likely destabilizing this intermediate by an out-of-plane distortion [28][34] and hence accelerating the cyclization. The dicationic

• indazole salt 5be was isolated in 30% yield and the benzyl-bridged, seven-membered salt 5bf could not be obtained under our optimized reaction conditions. Single crystal structures of selected salts were obtained to gain a better understanding of the bonding situation and the coordination states in these

• (method A): To a stirred solution of the corresponding (2-iodophenyl)-1H-benzo[d]imidazole or -indazole (200 µmol, 1.0 equiv) and mCPBA (85%, 44.8 mg, 220 µmol, 1.1 equiv) in DCM (1 mL) was added TfOH (44.2 µL, 500 µmol, 2.5 equiv) and the resulting solution was stirred for 72 h at 40 °C. The solvent was

Synthesis of N-phenyl- and N-thiazolyl-1H-indazoles by copper-catalyzed intramolecular N-arylation of ortho-chlorinated arylhydrazones

• Yara Cristina Marchioro Barbosa,
• Guilherme Caneppele Paveglio,
• Claudio Martin Pereira de Pereira,
• Sidnei Moura,
• Cristiane Storck Schwalm,
• Gleison Antonio Casagrande and
• Lucas Pizzuti

Beilstein J. Org. Chem. 2022, 18, 1079–1087, doi:10.3762/bjoc.18.110

• anticancer [2], anti-HIV [3], anti-inflammatory [4], antiprotozoal [5], antifungal [6], antibacterial [7], antiplatelet [8], and antihypertensive [9] properties. The relevance to medicinal chemistry is also demonstrated by the presence of the 1H-indazole core in the structure of drugs. The anticataract agent

• were applied to prepare a series of seven N-phenyl-1H-indazole derivatives, 2a,b,d–h, from o-chlorinated arylhydrazones 1a,b,d–h. The structure of the starting materials and products as well as the reaction conditions and yields are shown in Table 2. In general, the reactions were highly impacted by

• -substituted arylhydrazone 1b led to 2b in only 10% yield and 4-methoxy-substituted arylhydrazone 1c was not converted to the desired 1H-indazole 2c. Arylhydrazones 1d–f substituted with halogen atoms were converted in 23–53% yield, but for the 4-fluoro- and 5-fluoro-substituted substrates 1d and 1f, a longer

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

• combining thiazole, selenazole, pyrazole, indazole, and indole moieties with both carboxyl functional groups and cycloaminyl units [27][28][29][30][31]. In recent decades, various methods of constructing 1,2-oxazole ring systems have been developed [1][2][3][4][5][6][7][32]. The two primary pathways to 1,2

Regioselective N-alkylation of the 1H-indazole scaffold; ring substituent and N-alkylating reagent effects on regioisomeric distribution

• Ryan M. Alam and
• John J. Keating

Beilstein J. Org. Chem. 2021, 17, 1939–1951, doi:10.3762/bjoc.17.127

• , T12 YN60, Ireland 10.3762/bjoc.17.127 Abstract The indazole scaffold represents a promising pharmacophore, commonly incorporated in a variety of therapeutic drugs. Although indazole-containing drugs are frequently marketed as the corresponding N-alkyl 1H- or 2H-indazole derivative, the efficient

• synthesis and isolation of the desired N-1 or N-2 alkylindazole regioisomer can often be challenging and adversely affect product yield. Thus, as part of a broader study focusing on the synthesis of bioactive indazole derivatives, we aimed to develop a regioselective protocol for the synthesis of N-1

• alkylindazoles. Initial screening of various conditions revealed that the combination of sodium hydride (NaH) in tetrahydrofuran (THF) (in the presence of an alkyl bromide), represented a promising system for N-1 selective indazole alkylation. For example, among fourteen C-3 substituted indazoles examined, we

A straightforward conversion of 1,4-quinones into polycyclic pyrazoles via [3 + 2]-cycloaddition with fluorinated nitrile imines

• Greta Utecht-Jarzyńska,
• Karolina Nagła,
• Grzegorz Mlostoń,
• Heinz Heimgartner,
• Marcin Palusiak and
• Marcin Jasiński

Beilstein J. Org. Chem. 2021, 17, 1509–1517, doi:10.3762/bjoc.17.108

• stationary phase and either petroleum ether (or hexanes)/dichloromethane or petroleum ether/AcOEt mixtures as eluent to give analytically pure products 9a–h and 10c. 1-Phenyl-3-(trifluoromethyl)-1H-benzo[f]indazole-4,9-dione (9a) Reaction time 2 d; CC (SiO2, petroleum ether/CH2Cl2 2:1); 320 mg (93%); yellow

• -dihydro-1H-indazole-4,7-dione (10c) Reaction time 2 d; CC (SiO2, petroleum ether/AcOEt 20:1); 193 mg (53%); yellow oil; 1H NMR (CDCl3, 600 MHz) δ 1.39 (s, 3H, Me), 1.52 (qbr, J = 0.5 Hz, 3H, Me), 2.05–2.07 (m, 6H, 2 Me), 2.32 (s, 3H, Me), 6.95–6.97, 7.10–7.12 (2 m, 2H each, Tol); 13C NMR (CDCl3, 151 MHz

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• transition metal Lewis acids 291a–e that can coordinate to ketone substrates and form chiral photoactive complexes 292, which in many cases act as the in situ generated photocatalyst (Scheme 48) [115]. They have recently developed an example using an indazole-based ligand [116] to add to their well

Oxime radicals: generation, properties and application in organic synthesis

• Igor B. Krylov,
• Stanislav A. Paveliev,
• Alexander S. Budnikov and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107

• iminoxyl radical 90. Presumably, the radical 90 underwent cyclization involving the azo group to form indazole 91. During the photolysis of a mixture of di-tert-butyl peroxide with oxime 92 containing an alkenyl fragment at temperatures from −30 to −10 °C, two signals were observed in the EPR spectrum with

Reaction of indoles with aromatic fluoromethyl ketones: an efficient synthesis of trifluoromethyl(indolyl)phenylmethanols using K₂CO₃/n-Bu₄PBr in water

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati and
• Gregor Schnakenburg

Beilstein J. Org. Chem. 2020, 16, 778–790, doi:10.3762/bjoc.16.71

• -. 5-, 6-, and 7-azaindoles, 1g–j) provided the corresponding products in the range from 91–97% yield (3u–x). We applied the developed protocol to reactions of other heterocyclic systems such as indazole (4), benzimidazole (5), carbazole (6), benzofuran (7), and benzothiophene (8) with ketone 2a

Thermal stability of N-heterocycle-stabilized iodanes – a systematic investigation

• Andreas Boelke,
• Yulia A. Vlasenko,
• Mekhman S. Yusubov,
• Boris J. Nachtsheim and
• Pavel S. Postnikov

Beilstein J. Org. Chem. 2019, 15, 2311–2318, doi:10.3762/bjoc.15.223

• value among all investigated pseudocyclic iodanes (ΔHdec = 2.5 kJ/mol). Interestingly, the exothermal decomposition of 6 is superimposed by an endothermal melting process (Figure 3c). In direct comparison, indazole 8 is thermally less stable than 7 with a similar ΔHdec value. The throughout higher

• model reaction, especially N-substituted triazoles 4 and 5. In contrast, the reactivity of triazole 3 is comparable to that of benzoxazoles 13 and 14 as well as pyrazole 7 and indazole 8. In our view thiazole 12 is the best compromise in this regard since it is thermally even more stable than 7 and 8

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

• Andrew T. King,
• Hugh G. Hiscocks,
• Lidia Matesic,
• Mohan Bhadbhade,
• Roger Bishop and
• Alison T. Ung

Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134

• -butylnitrite, BTEAC and DABSO in the presence of CuCl2 provided an unexpected 3H-indazole product 8. The structure of the compound was determined by HRMS, IR, NMR and further confirmed by single crystal X-ray crystallography. The compound crystallises in the triclinic P-1 space group, with unit cell parameters

• OCH2–H···N interactions. In addition to these, there are Ar–H···H–Ar close contacts, (edge–edge and surrounding inversion centres) arranged as infinite tapes along the a direction. Keywords: Ar-H...H-Ar contact; [2 + 3] cycloaddition; diazo; 3H-indazole; X-ray structure; Introduction The use of

• . [12] (Scheme 1). Herein, we report the unexpected product derived from 5 under the reaction conditions described in Scheme 1. The unusual crystal packing present in this 3H-indazole product was also analysed. Results and Discussion The one-pot reaction of compound 5 with tert-BuONO and DABSO in the

Mn-mediated sequential three-component domino Knoevenagel/cyclization/Michael addition/oxidative cyclization reaction towards annulated imidazo[1,2-a]pyridines

• Olga A. Storozhenko,
• Alexey A. Festa,
• Delphine R. Bella Ndoutoume,
• Alexander V. Aksenov,
• Alexey V. Varlamov and
• Leonid G. Voskressensky

Beilstein J. Org. Chem. 2018, 14, 3078–3087, doi:10.3762/bjoc.14.287

• oxidative conditions has been developed. The employment of Mn(OAc)3·2H2O or KMnO4 as stoichiometric oxidants allowed the use of a wide range of nucleophiles, such as nitromethane, (aza)indoles, pyrroles, phenols, pyrazole, indazole and diethyl malonate. The formation of the target compounds presumably

[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

• -oxohexanoic acid with 4-fluoro-3-(4-methylphenyl)sydnone (Scheme 12). Unfortunately the regioselectivity of the reaction was not specified. An aryne generation (Scheme 13) was also used for the synthesis of a key intermediate of the potent antitumor PARP inhibitor – niraparib – containing an indazole core

Bromide-assisted chemoselective Heck reaction of 3-bromoindazoles under high-speed ball-milling conditions: synthesis of axitinib

• Jingbo Yu,
• Zikun Hong,
• Xinjie Yang,
• Yu Jiang,
• Zhijiang Jiang and
• Weike Su

Beilstein J. Org. Chem. 2018, 14, 786–795, doi:10.3762/bjoc.14.66

• Optimisation of chemical conditons At the commencement of the investigation, the cross-coupling between 3-bromo-1-methyl-1H-indazole (1a) and n-butyl acrylate (2a) was chosen as model reaction (Scheme 2). The initial attempts using our previous established conditions [24][25], gave only moderate conversion

• with a low yield of 53%. Noticeably, considerable amounts of 1-methyl-1H-indazole (4a) were obtained, which implicated the existence of a significant debromination process. As expected, the situation was more badly when the reaction was conducted under classic solvent-heating conditions (see Scheme S1

• coupling product 3oa (70%). Besides, N-unsubstituted indazole 1n could also be tolerated in this reaction giving 3na (52%) and 3nf (49%) in moderate yield by using 1,8-bis(dimethylamino)naphthalene as a base. To our delight, 3-chloroindazole could also be activated in this reaction, giving the

Multicomponent synthesis of spiropyrrolidine analogues derived from vinylindole/indazole by a 1,3-dipolar cycloaddition reaction

• Manjunatha Narayanarao,
• Lokesh Koodlur,
• Vijayakumar G. Revanasiddappa,
• Subramanya Gopal and
• Susmita Kamila

Beilstein J. Org. Chem. 2016, 12, 2893–2897, doi:10.3762/bjoc.12.288

• Krishnadevaraya University, Bellary-583105, India Department of Chemistry, University College of Science, Tumkur University, BH Road, Tumakuru-572103 India 10.3762/bjoc.12.288 Abstract A new series of spiropyrrolidine compounds containing indole/indazole moieties as side chains have been accomplished via a one

• -pot multicomponent synthesis. The method uses the 1,3-dipolar cycloaddition reaction between N-alkylvinylindole/indazole and azomethine ylides, prepared in situ from cyclic/acyclic amino acids. The 1,3-dipolar cycloaddition proceeds efficiently under thermal conditions to afford the regio- and

• in the construction of functionalized spiro compounds. We report herein the facile synthesis of novel spiropyrrolidine compounds through a one-pot three-component reaction involving N-substituted vinylindole/indazole, ninhydrin and sarcosine/L-proline. The present multicomponent reaction (MCR) leads

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

• -ylidenes spontaneously dimerize under ring cleavage of one of the N,N-bonds and ring closure to an indazole–indole spiro compound which possesses an exocyclic imine group. The E/Z isomers of the imines can be separated by column chromatography when methanol is used as eluent. We present results of a single

• crystal X-ray analysis of one of the E-isomers, which equilibrate in solution as well as in the solid state. Heating of the indazole–indole spiro compounds results in the formation of quinazolines by a ring-cleavage/ring-closure sequence (X-ray analysis). Results of DFT calculations are presented

• NHCs of indazole which have been generated and applied in heterocyclic synthesis (vide infra) as well as in complex chemistry [13]. Undoubtedly the N-heterocyclic carbenes of imidazole, imidazoline and the triazoles play the most important roles as ligands in metal-organic chemistry [14] or as

ML212: A small-molecule probe for investigating fluconazole resistance mechanisms in Candida albicans

• Willmen Youngsaye,
• Cathy L. Hartland,
• Barbara J. Morgan,
• Amal Ting,
• Partha P. Nag,
• Benjamin Vincent,
• Carrie A. Mosher,
• Joshua A. Bittker,
• Sivaraman Dandapani,
• Michelle Palmer,
• Luke Whitesell,
• Susan Lindquist,
• Stuart L. Schreiber and
• Benito Munoz

Beilstein J. Org. Chem. 2013, 9, 1501–1507, doi:10.3762/bjoc.9.171

• fungal cells. A substituted indazole possessing the desired bioactivity profile was selected for further development, and initial investigation of structure–activity relationships led to the discovery of ML212. Keywords: antifungal; Candida albicans; chemosensitizer; fluconazole; Molecular Libraries

• , these 29 candidates were tested once more in the entire assay tree outlined previously in Figure 1. Following this re-evaluation, methyl 3-phenyl-1H-indazole acetate (1, Figure 2) emerged as an attractive candidate for further development. A commercial sample of compound 1 shows good activity against

• closely related analogues were prepared to enable investigation of possible structure–activity relationships (SAR) [18]. In addition to indazole 1, two other structurally distinct scaffolds (2 and 3) were also selected for follow-up studies and those works are communicated elsewhere [19][20]. Chemistry

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

• . Indazole Pazopanib (246, Votrient) is a new potent multi-target tyrosine kinase inhibitor for various human cancer cell lines. Pazopanib is considered a promising replacement treatment to imatinib and sunitinib and was approved for renal cell carcinoma by the FDA in late 2009. The indazole system is built

• up via diazotisation and spontaneous cyclisation of 2-ethyl-5-nitroaniline (247) using tert-butyl nitrite. The resulting indazole structure 249 can be methylated entirely regioselectively with either Meerwein’s salt, trimethyl orthoformate or dimethyl sulfate. A tin-mediated reduction of the nitro