Cu(OTf)₂-catalyzed multicomponent reactions

• Sara Colombo,
• Camilla Loro,
• Egle M. Beccalli,
• Gianluigi Broggini and
• Marta Papis

Beilstein J. Org. Chem. 2025, 21, 122–145, doi:10.3762/bjoc.21.7

• formation releasing Cu(OTf)2. The final bicyclic product 33 arises from isomerization and water elimination. Recently, Singh's research group developed a cascade process to access imidazo[1,2-a]pyridines-linked isoxazoles 35. Isoxazole carbaldehydes treated with 2-aminopyridines and isonitriles in the

Synthesis of 2H-azirine-2,2-dicarboxylic acids and their derivatives

• Anastasiya V. Agafonova,
• Mikhail S. Novikov and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2024, 20, 3191–3197, doi:10.3762/bjoc.20.264

• chlorides have been developed. Keywords: azirine-2,2-dicarboxamides; azirine-2,2-dicarboxylic acids; isomerization; isoxazoles; Introduction The isomerization of isoxazoles, containing a heteroatomic substituent at C5, to 2H-azirines is a powerful method for the preparation of 2H-azirine-2-carboxylic acid

• the conversion of the latter to the acid chlorides 1 with thionyl chloride proceeded with yields of 77–92%. This made it possible to synthesize the target isoxazoles 1b,d,g–j with fairly high yields. Having in hand a set of isoxazoles 1a–i containing aryl substituents at the 3-position of the

• isoxazole ring, both with electron-donating and electron-withdrawing groups, and the tert-butyl-substituted isoxazole 1j, we proceeded to obtain dicarboxylic acids 6 (Scheme 2). The isomerization of isoxazoles 1 into diacyl chlorides 2 was achieved by applying the conditions for the isomerization of 3-aryl

Synthesis of spiroindolenines through a one-pot multistep process mediated by visible light

• Francesco Gambuti,
• Jacopo Pizzorno,
• Chiara Lambruschini,
• Renata Riva and
• Lisa Moni

Beilstein J. Org. Chem. 2024, 20, 2722–2731, doi:10.3762/bjoc.20.230

• cyclization of the indole derivatives is the most popular (Scheme 1a). For instance, the efficient synthesis of spiro[indoline-3,2′-pyrrolidines] [8][9][10] or spiro-isoxazoles [11] through different dearomatization processes has been reported. Recently, Ramana and Dothe have proposed an elegant gold

• the acid-catalyzed [4 + 1] cycloaddition of commercially available substrates, as indoles and nitroalkenes to give spiro-isoxazoles (Scheme 1c), but acceptable yields were obtained just using nitrostyrenes [13][14]. Despite these examples, the highly efficient construction of structurally diverse

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

• give 1,5-diacyl-5-hydroxypyrazolines 131. Cleavage of the protecting group with potassium carbonate in methanol finally provides the corresponding 5-acyl NH-pyrazoles 132 (Scheme 46) [149]. A novel approach to synthesizing pyrazoles via the initial formation of isoxazoles 138 through (3 + 2

Syntheses and medicinal chemistry of spiro heterocyclic steroids

• Laura L. Romero-Hernández,
• Ana Isabel Ahuja-Casarín,
• Penélope Merino-Montiel,
• Sara Montiel-Smith,
• José Luis Vega-Báez and
• Jesús Sandoval-Ramírez

Beilstein J. Org. Chem. 2024, 20, 1713–1745, doi:10.3762/bjoc.20.152

• synthesis of 2H-furan-3-ones from mestranol [23]. Initially, a 1,3-dipolar regioselective cycloaddition occurred between the alkyne group of mestranol and an alkanonitrile oxide generated in situ from the corresponding oxime, yielding isoxazoles 31. Later, a reductive ring cleavage of the isoxazole ring was

Synthesis of 1,2,3-triazoles containing an allomaltol moiety from substituted pyrano[2,3-d]isoxazolones via base-promoted Boulton–Katritzky rearrangement

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

Beilstein J. Org. Chem. 2024, 20, 1334–1340, doi:10.3762/bjoc.20.117

• to the considered rearrangement of isoxazoles containing an hydrazone unit. In this case the studied process results in formation of corresponding 1,2,3-triazoles with carbonyl moiety (Scheme 1a) [16][17][18][19]. Despite the wide variety of described recyclizations of this type for diverse

Mild and efficient synthesis and base-promoted rearrangement of novel isoxazolo[4,5-b]pyridines

• Vladislav V. Nikol’skiy,
• Mikhail E. Minyaev,
• Maxim A. Bastrakov and
• Alexey M. Starosotnikov

Beilstein J. Org. Chem. 2024, 20, 1069–1075, doi:10.3762/bjoc.20.94

• either annulation of an isoxazole fragment to a pyridine cycle or vice versa formation of a pyridine ring based on appropriately substituted isoxazoles. In the first case (Scheme 1A) 3-halo- [11][15][16][17][18][19] or 3-hydroxypyridines [8][20] bearing a suitable functionality in position 2 were used

• for the cyclization. Alternatively (Scheme 1B), isoxazolo[4,5-b]pyridines can be constructed via intramolecular cyclization of 4-(propargylamino)isoxazoles [21] or through reactions of 4-amino-5-benzoylisoxazoles with ketones or 1,3-dicarbonyl compounds [10][13]. These and some additional examples of

• -b]pyridine took place, followed by a base-promoted decarbonylation/isoxazole ring opening. Such transformations have been previously reported for benzo[d]isoxazoles with a carbonyl or carboxyl group in position 3 or 3-unsubstituted benzo[d]isoxazoles [25][26][27][28][29]. This means that the formyl

Synthetic approach to 2-alkyl-4-quinolones and 2-alkyl-4-quinolone-3-carboxamides based on common β-keto amide precursors

• Yordanka Mollova-Sapundzhieva,
• Plamen Angelov,
• Danail Georgiev and
• Pavel Yanev

Beilstein J. Org. Chem. 2023, 19, 1804–1810, doi:10.3762/bjoc.19.132

• reductive cyclizations of o-nitrobenzoyl ketones [57][58], enamines [59][60], or isoxazoles [61]. The scope of these reductive cyclizations is limited by the availability of the necessary intermediates and has remained largely underexplored, especially with regard to 4-quinolones with long-chain

Lewis acid-promoted direct synthesis of isoxazole derivatives

• Dengxu Qiu,
• Chenhui Jiang,
• Pan Gao and
• Yu Yuan

Beilstein J. Org. Chem. 2023, 19, 1562–1567, doi:10.3762/bjoc.19.113

• nitrogen source (Scheme 1, reaction 2). In 2017, Xu and co-workers [19] developed a copper-mediated annulation reaction to synthesize isoxazoles from two different alkynes. In fact, most methods mostly used highly toxic transition-metal catalysts such as copper metals. In order to develop cheaper and more

• molecules containing isoxazole moieties. Crystal structure of 3i. Traditional methods for the synthesis of isoxazoles and the current approach. Reaction scope of alkynes. Conditions: 1 (0.1 mmol, 1 equiv), 2a (0.2 mmol, 2 equiv), AlCl3 (0.3 mmol, 3 equiv), NaNO2 (1 mmol, 10.0 equiv), DMAc (1.0 mL), N2

N-Sulfenylsuccinimide/phthalimide: an alternative sulfenylating reagent in organic transformations

• Fatemeh Doraghi,
• Seyedeh Pegah Aledavoud,
• Mehdi Ghanbarlou,
• Bagher Larijani and
• Mohammad Mahdavi

Beilstein J. Org. Chem. 2023, 19, 1471–1502, doi:10.3762/bjoc.19.106

• , chalcogensuccinimide as an electrophile, and cyclopropane as a zwitterion component (Scheme 21) [58]. In 2020, a Lewis acid-mediated cyclization of β,γ-unsaturated oximes 51 and hydrazones 52 with N-(arylsulfenyl)succinimide 1 and N-(arylseleno)succinimide 1’’ was extended for the formation of isoxazoles 53 and

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

• substrate scope was achieved by varying the substituents in the C3 position of the isoxazoles 82 and the carbocyclic ring substituents in ketimines 49. Few more products were added to the library by altering the substituents of the amine in 82 and the ring nitrogen in 49 (Scheme 20a) [48]. The

An isoxazole strategy for the synthesis of 4-oxo-1,4-dihydropyridine-3-carboxylates

• Timur O. Zanakhov,
• Ekaterina E. Galenko,
• Mikhail S. Novikov and
• Alexander F. Khlebnikov

Beilstein J. Org. Chem. 2022, 18, 738–745, doi:10.3762/bjoc.18.74

• derivatives of 4-oxo-1,4-dihydropyridine-3-carboxylic acid 2 via Mo(CO)6-mediated rearrangement of methyl 2-(isoxazol-5-yl)-3-oxopropanoates 1 (Scheme 1). Results and Discussion Based on our experience of using isoxazoles in the synthesis of heterocyclic compounds [14][15][16][17][18], we hypothesized that

• isoxazoles 1 can undergo reductive ring opening under the action of Mo(CO)6/H2O/MeCN [14][19][20][21][22][23] to enamines 3, which can be cyclized on acyl R3C(O) group to form pyridones 2 (Scheme 2, route a). The alternative cyclization scenario, which may involve the ester group of enamine 3 and lead to the

• , resulted from the deacylation of intermediate 3g, was isolated in the reaction carried out at 70 °C. This side process is probably the reason for the decrease in the yield of the target pyridone 2g. Considering that isoxazoles were previously reduced to enaminones by other reducing systems [24][25][26][27

Synthesis of 3,4,5-trisubstituted isoxazoles in water via a [3 + 2]-cycloaddition of nitrile oxides and 1,3-diketones, β-ketoesters, or β-ketoamides

• Md Imran Hossain,
• Md Imdadul H. Khan,
• Seong Jong Kim and
• Hoang V. Le

Beilstein J. Org. Chem. 2022, 18, 446–458, doi:10.3762/bjoc.18.47

• Agriculture, Agricultural Research Service, University of Mississippi, Mississippi 38677, USA 10.3762/bjoc.18.47 Abstract Herein we report a method for the synthesis of 3,4,5-trisubstituted isoxazoles in water under mild basic conditions at room temperature via a [3 + 2]-cycloaddition of nitrile oxides and

• 1,3-diketones, β-ketoesters, or β-ketoamides. We optimized the reaction conditions to control the selectivity of the production of isoxazoles and circumvent other competing reactions, such as O-imidoylation or hetero [3 + 2]-cycloaddition. The reaction happens fast in water and completes within 1–2

• hours, which provides an environmentally friendly access to 3,4,5-trisubstituted isoxazoles, an important class of structures found in numerous bioactive natural products and pharmaceuticals. Additionally, we optimized the reaction conditions to produce trifluoromethyl-substituted isoxazoles, a

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

• analysis, 1H, 13C, and 15N NMR spectroscopy, HRMS, and single-crystal X-ray diffraction data. Keywords: β-enamino ketoesters; heterocyclic amino acids; 15N-labeled 1,2-oxazole; NMR (1H; 13C; 15N); 1,2-oxazole (isoxazole); X-ray structure analysis; Introduction 1,2-Oxazoles (isoxazoles) constitute an

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

Regioselective synthesis of heterocyclic N-sulfonyl amidines from heteroaromatic thioamides and sulfonyl azides

• Vladimir Ilkin,
• Vera Berseneva,
• Tetyana Beryozkina,
• Tatiana Glukhareva,
• Lidia Dianova,
• Wim Dehaen,
• Eugenia Seliverstova and
• Vasiliy Bakulev

Beilstein J. Org. Chem. 2020, 16, 2937–2947, doi:10.3762/bjoc.16.243

• -arylamino-1,2,3-triazole-4-N-sulfonylcarbimidamides. 2,5-Dithiocarbamoylpyridine reacts with sulfonyl azides to form a pyridine bearing two sulfonyl amidine groups. Keywords: amidines; Dimroth rearrangement; isoxazoles; sulfonyl thiazoles; thioamides; 1,2,3-triazoles; Introduction The biological activity

Synthesis of new fluorescent molecules having an aggregation-induced emission property derived from 4-fluoroisoxazoles

• Kazuyuki Sato,
• Akira Kawasaki,
• Yukiko Karuo,
• Atsushi Tarui,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2020, 16, 1411–1417, doi:10.3762/bjoc.16.117

• heteroaromatic systems, especially those comprising two heteroatoms such as pyrazoles [28][29], isoxazoles [30], and thiazoles [31][32]. Recently, we reported the selective fluorination of isoxazoles, to give monofluorinated isoxazoles 3 or trifluorinated isoxazolines 4 in moderate to good yields (Scheme 1) [33

• fluorescent luminescence characteristics of 4-fluoroisoxazoles, the synthesis of α-fluorinated boron ketoiminates (F-BKIs), and their photochemical properties. Results and Discussion Synthesis and optical properties of 4-fluorinated isoxazoles Although there is a large number of fluorescent molecules

• fluorescent properties by irradiation with a UV lamp. Among the non-fluorinated isoxazoles, only 2c demonstrated fluorescent emission, although it was very weak. Thus, we decided to further investigate the photochemical properties and the results were summarized in Figure 1 and Table 1. Introducing a fluorine

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

• or 61). As a result of the reaction, a 5-membered cycle is formed via the formation of C–O (products 58 and 60) or C–N bond (product 61) in accordance with the ability of oxime radicals to act as O- or N-radicals. The formation of the heterocycles, mainly isoxazolines/isoxazoles, from unsaturated

• the β-position were transformed into isoxazolines or isoxazoles by oxidative cyclization [114] under the action of TEMPO and K2CO3 (Scheme 23). The presence of aryl substituents at the β-position of the oxime contributed to high yields of the desired products (63a–c, 55–87%), in the presence of only

• one aryl group in the β-position (R3 = H, R2 = Ar) and further processing of the reaction mixture with atmospheric oxygen, an aromatization occurs with the formation of isoxazoles (64a,b 55–95%). Presumably, the reaction of TEMPO with oxime 62 affords the iminoxyl radical 65 (Scheme 24). 1,5-HAT in

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

• commercialized and applied in the agrochemical industry. These herbicides are mainly divided into three categories: triketones, pyrazoles, and isoxazoles [9][15][16]. Figure 1 shows some HPPD-inhibiting herbicides, namely mesotrione, tefuryltrione, isoxaflutole, topramezone, and pyrasulfotole. Among them

The use of isoxazoline and isoxazole scaffolding in the design of novel thiourea and amide liquid-crystalline compounds

• Itamar L. Gonçalves,
• Rafaela R. da Rosa,
• Vera L. Eifler-Lima and
• Aloir A. Merlo

Beilstein J. Org. Chem. 2020, 16, 175–184, doi:10.3762/bjoc.16.20

• study of gels derived from low molecular mass gelators [15][16], and consequently the investigation of gelators of low molar mass with liquid crystal proprieties remains active [17][18]. In addition, isoxazolines and isoxazoles have been identified as promising templates in liquid crystal development

• differential scanning calorimetry (DSC). Results and Discussion Synthesis In order to generate molecular structural diversity in thioureas, three sets of amines carrying 5-membered isoxazolines/isoxazoles (see Scheme 1) were employed and condensed with acyl isothiocyanates, as outlined in Scheme 2. Amines 3, 4

• containing isoxazoline rings 17a–c and isoxazoles 18a–c, as well as LCs amides 19–22 and 24. All compounds listed in Table 1 are capable of self-organization by hydrogen bonds, either in their solid state or in solution. Solubility in protic or aprotic polar solvent is restricted at room temperature. However

AgNTf₂-catalyzed formal [3 + 2] cycloaddition of ynamides with unprotected isoxazol-5-amines: efficient access to functionalized 5-amino-1H-pyrrole-3-carboxamide derivatives

• Ziping Cao,
• Jiekun Zhu,
• Li Liu,
• Yuanling Pang,
• Laijin Tian,
• Xuejun Sun and
• Xin Meng

Beilstein J. Org. Chem. 2019, 15, 2623–2630, doi:10.3762/bjoc.15.255

• carbene pathway presumed by mechanistic studies and theoretical calculations. Following our ongoing interest in the alkyne chemistry [36][37][38], we recently envisaged that the reaction of ynamides with isoxazoles could proceed under silver catalysis conditions, involving the generation of α-imino silver

• can enhance the nucleophilic ability of nitrogen on the isoxazole ring. However, this change could raise at least an issue, involving the direct addition of an amino motif to the ynamide substrate [43][44]. To answer this question, two isoxazoles 7 and 8a with an amino group at the distinct position

• . Reactions of ynamides or ynol ethers with isoxazoles by transition metal catalysis. Reactions of ynamide 4a with different isoxazoles 5, 7 and 8a. A gram-scale experiment. Mechanistic hypotheses for Ag-catalyzed reaction of ynamide 4a with aminoisoxazole 8a. Possible reaction routes of intermediate C

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via intramolecular 1,3-dipolar cycloaddition

• Yulia V. Khoroshunova,
• Denis A. Morozov,
• Andrey I. Taratayko,
• Polina D. Gladkikh,
• Yuri I. Glazachev and
• Igor A. Kirilyuk

Beilstein J. Org. Chem. 2019, 15, 2036–2042, doi:10.3762/bjoc.15.200

• loss of a hydrogen atom is consistent with the susceptibility of 7c to oxidative decay (Scheme 3). Intramolecular cycloaddition of similar nitrones is known to lead to hexahydro-1H-cyclopenta[c]isoxazoles [6][12]. Indeed, heating of 7а–с at 145 °C in toluene for 30–60 min in a microwave oven produced

Isoxazole derivatives as new nitric oxide elicitors in plants

• Anca Oancea,
• Emilian Georgescu,
• Florentina Georgescu,
• Alina Nicolescu,
• Elena Iulia Oprita,
• Catalina Tudora,
• Lucian Vladulescu,
• Marius-Constantin Vladulescu,
• Florin Oancea and
• Calin Deleanu

Beilstein J. Org. Chem. 2017, 13, 659–664, doi:10.3762/bjoc.13.65

• Centre of Organic Chemistry, Romanian Academy, Spl. Independentei 202-B, RO-060023 Bucharest, Romania National Research & Development Institute for Chemistry & Petrochemistry – ICECHIM, Spl. Independentei 202, RO-060021 Bucharest, Romania 10.3762/bjoc.13.65 Abstract Several 3,5-disubstituted isoxazoles

• -disubstituted isoxazoles on nitric oxide and reactive oxygen species generation in Arabidopsis tissues was studied using specific diaminofluoresceine dyes as fluorescence indicators. Keywords: chemical elicitor; 1,3-dipolar cycloaddition; isoxazole; nitric oxide; nitrile oxide; reactive oxygen species

• ; Introduction Isoxazoles are an interesting class of N-heterocyclic compounds intensely studied mainly due to their wide range of biological activity [1][2]. Isoxazole compounds show antiviral [3][4], antithrombotic [5][6][7][8][9], analgesic [9], COX-2 inhibitory [10][11], anti-inflamatory [9][11

Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

• Ilya V. Efimov,
• Marsel Z. Shafikov,
• Nikolai A. Beliaev,
• Natalia N. Volkova,
• Tetyana V. Beryozkina,
• Wim Dehaen,
• Zhijin Fan,
• Viktoria V. Grishko,
• Gert Lubec,
• Pavel A. Slepukhin and
• Vasiliy A. Bakulev

Beilstein J. Org. Chem. 2016, 12, 2390–2401, doi:10.3762/bjoc.12.233

• -5-substituted isoxazoles that are otherwise difficult to obtain. Keywords: β-azolyl enamine; [3 + 2]-cycloaddition; isoxazole; isoxazoline; nitrile oxide; Introduction The biological activity and technically useful properties of isoxazoles have made them the focus of both medicinal and materials

• chemistry over the years [1]. Isoxazoles have been found in natural products [1], and they exhibit anticancer [2], antiviral [1], anti-inflammatory [3], antidiabetic [4], anti-Alzheimer [5] and many other types of biological activity [6]. Isoxazolines and isoxazoles have been applied as chemosensors, liquid

• crystalline compounds, ligands for asymmetric synthesis, and they are also convenient reagents in organic synthesis [1]. Although bicyclic assemblies of azoles exhibit interesting chemical properties and biological activities [1][7][8][9][10][11] isoxazoles conjugated to other azole rings are poorly presented

Synthesis of 2,1-benzisoxazole-3(1H)-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

• Daria Yu. Dzhons and
• Andrei V. Budruev

Beilstein J. Org. Chem. 2016, 12, 874–881, doi:10.3762/bjoc.12.86

• ethanol. As can be seen in Table 3, the photolysis of 1c,d in a 1,4-dioxane/water mixture under these conditions lead to decreased yields of 2c,d and to the formation of azepine 3c and primary amines 4c,d with significant yields. An explanation for the decreased yields observed for isoxazoles 2c,d may be