Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• state 98). The substrate scope comprised mainly varying aryl or heteroaryl-substituents at the alkyne moiety that imparted high degrees of enantioselectivities to the products (Scheme 22b) [52]. In 2022, Huang and co-workers demonstrated an atroposelective construction of 3,4’-indole-pyrazole frameworks

• electrophilic substitution also gave a quaternary aza-stereocenter in the pyrazolone moiety. Axial chirality associated with central chirality in the product structures was influenced by chiral phosphoric acid catalyst P23. To freeze the C–C bond rotation, the pyrazole moiety in 99 required sterically demanding

• rigidity in the corresponding transition state (Scheme 23) [53]. In 2023, a chiral phosphoric acid ent-P17-mediated aza-Friedel–Crafts alkylation was reported between 5-aminopyrazole 92 as the π-nucleophile and 3H-indol-3-ones 69 as electrophilic reagents. The presence of an amino group in pyrazole 92 is

Facile access to 3-sulfonylquinolines via Knoevenagel condensation/aza-Wittig reaction cascade involving ortho-azidobenzaldehydes and β-ketosulfonamides and sulfones

• Ksenia Malkova,
• Andrey Bubyrev,
• Stanislav Kalinin and
• Dmitry Dar’in

Beilstein J. Org. Chem. 2023, 19, 800–807, doi:10.3762/bjoc.19.60

• substrate scope for the protocol proposed were found out during the course of the study. Indole- and pyrazole-based azidoaldehydes 1r and 1s failed to provide the desired compounds 5r and 5s (Scheme 4). The reaction stopped on the iminophosphorane formation and did not progress further likely due to

Synthesis of substituted 8H-benzo[h]pyrano[2,3-f]quinazolin-8-ones via photochemical 6π-electrocyclization of pyrimidines containing an allomaltol fragment

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky,
• Mikhail E. Minyaev and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2023, 19, 778–788, doi:10.3762/bjoc.19.58

• -1,2-diketone [21][22][23][24][25]. However, the direction of the transformation in each case depends on the structure of the bridge fragment. Thus, for example, the 1,3,5-hexatriene cyclization does not occur for pyrazole 1 and imidazole 2 derivatives, and the obtained products are formed exclusively

Strategies in the synthesis of dibenzo[b,f]heteropines

• David I. H. Maier,
• Barend C. B. Bezuidenhoudt and
• Charlene Marais

Beilstein J. Org. Chem. 2023, 19, 700–718, doi:10.3762/bjoc.19.51

• ) cyclised products. 3.3 Ullmann-type coupling Copper-catalysed Ullmann etherification (Scheme 20) offers an alternative to SNAr and Buchwald–Hartwig etherification. Olivera et al. [61] reported a copper-catalysed Ullmann-type etherification as a key step in the synthesis of their pyrazole-fused dibenzo[b,f

Enolates ambushed – asymmetric tandem conjugate addition and subsequent enolate trapping with conventional and less traditional electrophiles

• Péter Kisszékelyi and
• Radovan Šebesta

Beilstein J. Org. Chem. 2023, 19, 593–634, doi:10.3762/bjoc.19.44

• functional group tolerance with excellent stereoselectivities. In 2016, Ellman and co-workers demonstrated a Rh- or Co-catalyzed highly diastereoselective tandem C–H bond addition/aldol reaction sequence [96][97]. The C–H activation was promoted by pyridine, pyrazole, or imine directing groups, while the

Transition-metal-catalyzed C–H bond activation as a sustainable strategy for the synthesis of fluorinated molecules: an overview

• Louis Monsigny,
• Floriane Doche and
• Tatiana Besset

Beilstein J. Org. Chem. 2023, 19, 448–473, doi:10.3762/bjoc.19.35

• ) were found to be suitable substrates leading to the corresponding products 12h and 12i in 91% and 83% yields, respectively. The use of other directing groups was also suitable for this transformation such as methyl and cyano-substituted pyridines 13a,b, pyrimidine (13c), pyrazole (13d), as well as the

• % yield, 19a, 84% yield), substituted pyrazole derivatives (6 examples, up to 55% yield, 19b, 55% yield), pyrimidine (19c, 31% yield) as well as quinoline and isoquinoline (19d and 19e, 65% and 66% yields, respectively). In addition, the trifluoromethylthiolated benzo[h]quinoline 20f was obtained in good

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

• benzimidazoles gave the expected products 5an–ap in 50–60% yield. The pyrazole-substituted salt 5aq was obtained with 65% yield. Using an electron-rich 5,6-dimethylbenzimidazole substrate yielded dimethylated product 5ar in 85% yield. Unfortunately, even under harsher reaction conditions, the corresponding

• . Next, the iodonium center was stabilized through an additional N-coordination via ortho-pyrazole substitution, giving the iodonium salts 5ba and 5bb in 88% and 50% yield. When replacing imidazoles by indazoles the oxidation was not as efficient giving the products 5bc and 5bd with only 24% and 44

• novel azoiodazinium salts (Figure 3). An N4–I1 distance of 2.540 Å with a typical T-shape structure (N4–I1–C1 angle 185.74°) implies a significant interaction between the N-heterocycle and the iodine atom for the ortho-pyrazole-substituted derivative 5bb [35]. However, the presence of an ortho-methyl

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

• Department of Chemistry, Central University of Punjab, Bathinda, 151401, Punjab, India, Department of Chemistry, National Institute of Technology (NIT) Manipur, Imphal, 795004, India 10.3762/bjoc.19.22 Abstract An operationally simple and metal-free approach is described for the synthesis of pyrazole

• -tethered thioamide and amide conjugates. The thioamides were generated by employing a three-component reaction of diverse pyrazole C-3/4/5 carbaldehydes, secondary amines, and elemental sulfur in a single synthetic operation. The advantages of this developed protocol refer to the broad substrate scope

• , metal-free and easy to perform reaction conditions. Moreover, the pyrazole C-3/5-linked amide conjugates were also synthesized via an oxidative amination of pyrazole carbaldehydes and 2-aminopyridines using hydrogen peroxide as an oxidant. Keywords: C–S/O bond formation; metal-free; oxidative amidation

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• with amino and nitro groups due to side processes on the electrodes. Cyclic carbamates were oxidized to lactams using ABNO derivatives as electrocatalysts [104] (Scheme 16A). The substrates with easily oxidizable pyrazole and oxazole fragments reacted successfully under these conditions. Under similar

A study of the photochemical behavior of terarylenes containing allomaltol and pyrazole fragments

• Constantine V. Milyutin,
• Andrey N. Komogortsev,
• Boris V. Lichitsky and
• Valeriya G. Melekhina

Beilstein J. Org. Chem. 2022, 18, 588–596, doi:10.3762/bjoc.18.61

• -pyranone containing terarylenes with a pyrazole bridge fragment were studied. It was shown that UV-induced 6π-electrocyclization of the 1,3,5-hexatriene system was not observed for the considered objects molecules. At the same time, the phototransformation of such systems proceeds exclusively in the

• -phenylenediamine. The general method for the preparation of the corresponding quinoxalines on the basis of the aforementioned condensation was implemented. It was demonstrated that the studied photoreaction does not depend on the type of pyrazole bridge. The structures of three of synthesized products were

• bifunctional objects provides access to novel UV irradiation-based synthetic methods. Continuing our studies devoted to the photochemistry of terarylenes [27][28][29][30][31][32], in this communication we studied the UV-promoted reaction of pyrazole derivatives 12 containing a 3-hydroxypyran-4-one fragment

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

• -nitro-1H-pyrazoles bearing a dichloromethyl and an amino or thio moiety at C3 and C5 has been prepared in yields up to 72% from the reaction of 1,1-bisazolyl-, 1-azolyl-1-amino-, and 1-thioperchloro-2-nitrobuta-1,3-dienes with 7-chloro-4-hydrazinylquinoline. A new way for the formation of a pyrazole

• position 1 of the pyrazole ring with the aim to obtain new compounds with antimalarial and/or anti-SARS-CoV activity. Polyhalo-1,3-butadienes, carrying at least one nitro group, are valuable starting materials for the directed synthesis of highly functionalized heterocycles. During the past years, we have

• with four different substituents: in position 1 of the pyrazol cycle a 7-chloroquinolin-4-yl unit, in position 3 various amino or thio fragments, in position 4 a nitro and in position 5 a dichloromethyl group. Some biological activities of 7-chloroquinolinyl-substituted pyrazole derivatives have

Synthesis of novel [1,2,4]triazolo[1,5-b][1,2,4,5]tetrazines and investigation of their fungistatic activity

• Anna V. Korotina,
• Svetlana G. Tolshchina,
• Rashida I. Ishmetova,
• Natalya P. Evstigneeva,
• Natalya A. Gerasimova,
• Natalya V. Zilberberg,
• Nikolay V. Kungurov,
• Gennady L. Rusinov,
• Oleg N. Chupakhin and
• Valery N. Charushin

Beilstein J. Org. Chem. 2022, 18, 243–250, doi:10.3762/bjoc.18.29

• can also be used as an oxidant for the oxidation of benzamidine derivatives 2b,c in acetonitrile under microwave irradiation. Along with the cyclization reaction, bromination of the pyrazole ring proved to occur at position C(4) to give the products 3j,k, as evidenced by disappearance of the

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

• 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

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

• have a major influence on the outcome of the reaction: (1) the addition of side chains R1 to the core pyrazole ring system, which can occur in position N-6 or N-7, and (2) the cyclative cleavage of the triazene group of compounds 9 and 10 which should lead to the target compounds 5 and 6. To carry out

Recent advances in the asymmetric phosphoric acid-catalyzed synthesis of axially chiral compounds

• Alemayehu Gashaw Woldegiorgis and
• Xufeng Lin

Beilstein J. Org. Chem. 2021, 17, 2729–2764, doi:10.3762/bjoc.17.185

• produce an ion-pair interaction with CPA 15 in addition to the hydrogen-bonding interaction. 2.2. Synthesis of miscellaneous atropisomeric heterobiaryls Axially chiral pyrazole scaffolds are commonly found in natural products and drugs and are often used as valuable building blocks in organic synthesis

• [69]. Herein, Li and co-workers developed a new asymmetric synthesis of atropisomeric pyrazole derivatives 56 via an enantioselective reaction of azonaphthalene 54 with pyrazolone 55 using 5 mol % chiral phosphoric acid CPA 16. Substrates bearing electron-donating and electron-withdrawing groups gave

• the desired axially chiral pyrazole derivatives 56 in good yields (up to 99%) with excellent enantioselectivities (up to 98% ee, Scheme 19). Density functional theory calculations revealed that the chiral phosphoric acid acts as a proton-transfer shuttle to assist proton transfer from the OH group of

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

• electrophiles, while maintaining a high degree of N-1 regioselectivity. Keywords: indazole; N-alkylation; regioselective; sodium hydride; tetrahydrofuran; Introduction Indazole (benzo[c]pyrazole) is an aromatic bicyclic heterocycle and can be viewed as a (bio)isostere of indole [1]. While only a few naturally

• , respectively (Table 2, entry 3). Apart from the 1H-indazole scaffold [36][37], the steric influence of adjacent substituent(s) on N-alkylation regioselectivity has previously been described for other nitrogen-containing heterocycles, such as pyrazole [38], purine, and related 1,3-azoles [39]. Although the N

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

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

• fused pyrazole derivatives as the exclusive products. The reactions proceed via the initially formed [3 + 2]-cycloadducts, which undergo spontaneous aerial oxidation to give aromatized heterocyclic products. Only for 2,3,5,6-tetramethyl-1,4-benzoquinone, the expected [3 + 2]-cycloadduct exhibited fair

• considerable attention of other groups [18][19] and recently has been applied for the preparation of some π-extended pyrazole derivatives, which exhibited promising biological activity [20]. In a series of our recent publications, efficient syntheses of fluoromethylated five- and six-membered N,S-heterocycles

• respective hydrazonoyl bromides 8 and smoothly undergo [3 + 2]-cycloadditions with both electron-rich C=C dipolarophiles [27][28][29] and arynes [30], yielding the corresponding pyrazole derivatives. Unexpectedly, they reacted also with electron-deficient polyfluorinated thioamides to give the desired 1,3,4

Double-headed nucleosides: Synthesis and applications

• Vineet Verma,
• Jyotirmoy Maity,
• Vipin K. Maikhuri,
• Ritika Sharma,
• Himal K. Ganguly and
• Ashok K. Prasad

Beilstein J. Org. Chem. 2021, 17, 1392–1439, doi:10.3762/bjoc.17.98

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• alkylbiguanides with yields up to 97%, despite great variability in the case of alkylbiguanides (Scheme 8A) [24]. Recently, Zhou et al. reported similar conditions applied for the synthesis of anticancer biguanides [25]. The conditions chosen for the synthesis of a small library of pyrazole‐containing biguanide

• can act as a “bisamidine transfer agent” by the addition of an amine, and subsequent elimination of the leaving group. Two types of “biguanide transfer agents” have been developed so far. Depending on the nature of the leaving group they can be separated into either pyrazole or thiomethyl agents

• -amidinopyrazole hydrochloride from cyanoguanidine, by the addition of pyrazole hydrochloride in refluxing pyridine, refluxing 3 M aqueous HCl or by a direct fusion at 140–200 °C (no yields disclosed) [66]. Later in 1992, Bernatowicz et al., in an attempt to produce guanidine derivatives of ornithine-containing

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

Synthesis of bis(aryloxy)fluoromethanes using a heterodihalocarbene strategy

• Carl Recsei and
• Yaniv Barda

Beilstein J. Org. Chem. 2021, 17, 813–818, doi:10.3762/bjoc.17.70

• . Unfortunately, several methods of halodecarboxylation [11][12][13] failed to yield the desired product 10 (X = Cl, Br), likely due to the presence, in the pyrazole, of moieties sensitive to these conditions or to the instability of the product to the reaction conditions. Pursuing the heterodihalocarbene

Effective microwave-assisted approach to 1,2,3-triazolobenzodiazepinones via tandem Ugi reaction/catalyst-free intramolecular azide–alkyne cycloaddition

• Maryna O. Mazur,
• Oleksii S. Zhelavskyi,
• Eugene M. Zviagin,
• Svitlana V. Shishkina,
• Vladimir I. Musatov,
• Maksim A. Kolosov,
• Elena H. Shvets,
• Anna Yu. Andryushchenko and
• Valentyn A. Chebanov

Beilstein J. Org. Chem. 2021, 17, 678–687, doi:10.3762/bjoc.17.57

• molecular frameworks in medicinal chemistry. Of these, 1,4-benzodiazepines fused with pyrazole or triazole cycles are the base for many drugs (Figure 1) [1]. The spectrum of their biological activity includes tranquilizing, muscular relaxant, anticonvulsant, and sedative effects [2]. The general application

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

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

• the hexahydropyrazolo[1,2-a]pyrazole ring, respectively, apparently through zwitterionic intermediates [28][29]. At the same time, the cycloaddition of azomethine imine to 1,3-diphenylprop-2-en-1-ones (chalcones) in IL proceeds stereo- and regioselectively giving two diastereomeric bicyclic anti