Transition-metal-free intramolecular Friedel–Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives

• Tülay Yıldız,
• İrem Baştaş and
• Hatice Başpınar Küçük

Beilstein J. Org. Chem. 2021, 17, 2203–2208, doi:10.3762/bjoc.17.142

• gold(III) [43], iridium(III) [44][45], iron(III) [46], or bismuth(III) [47][48] were used as catalysts for the intermolecular hydroarylation of unactivated alkenes. Organic Brønsted acids were also used as catalysts in a smaller number of studies [49][50]. In this work, we searched for some organic

• Brønsted acids and Lewis acids as catalysts (Table 1) to develop an intramolecular FCA protocol with activating alkenes effectively and economically in order to obtain some originally substituted arylxanthenes under mild conditions for the first time. We found that, among these acids, trifluoroacetic acid

• development trials for the synthesis of xanthene derivatives were carried out. For this purpose, catalyst researches were carried out using compound 4a. An intramolecular Friedel–Crafts reaction was tried by activating the alkene with various organic Brønsted acids and Lewis acids (Table 1). In the reaction

Chemical syntheses and salient features of azulene-containing homo- and copolymers

• Vijayendra S. Shetti

Beilstein J. Org. Chem. 2021, 17, 2164–2185, doi:10.3762/bjoc.17.139

• dehalogenative polycondensation reaction of 1,3-dibromoazulene (4) by an organonickel catalyst (Yamamoto protocol) yielded 1,3-polyazulene 5. The polymer was partially soluble in many organic solvents such as chloroform, THF, xylenes, DMF, N-methylpyrrolidone (NMP), and also in Brønsted acids like TFA and conc

Asymmetric organocatalyzed synthesis of coumarin derivatives

• Natália M. Moreira,
• Lorena S. R. Martelli and
• Arlene G. Corrêa

Beilstein J. Org. Chem. 2021, 17, 1952–1980, doi:10.3762/bjoc.17.128

• stereogenic centers. Review A plethora of highly effective small‐molecule organocatalysts have enriched the field of organic synthesis [27], including chiral proline derivatives, N‐heterocyclic carbenes, chiral thioureas and Brønsted acids as well as phase‐transfer catalysts (PTC), such as the quaternary

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

• described how attempts to synthesize 22-1 proved to be unsatisfactory [42] and in 1995, they reported their synthesis characterized only by 19F NMR and described that the salts were moisture-sensitive [84]. The synthesis is sensitive to solvents and the amount of Brønsted acids (HX). N,N’-Difluoro-1,4

Iodine-catalyzed electrophilic substitution of indoles: Synthesis of (un)symmetrical diindolylmethanes with a quaternary carbon center

• Thanigaimalai Pillaiyar,
• Masoud Sedaghati,
• Andhika B. Mahardhika,
• Lukas L. Wendt and
• Christa E. Müller

Beilstein J. Org. Chem. 2021, 17, 1464–1475, doi:10.3762/bjoc.17.102

• derivatives have recently received increasing attention from synthetic organic chemists, biologists, and pharmacologists. In general, DIMs can be synthesized via electrophilic substitution of indoles by aldehydes or ketones in the presence of conventional Lewis or Brønsted acids as catalysts [19]. This

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• ion, which was followed by a completely diastereoselective Friedel–Crafts reaction (Scheme 70). List and co-workers devised a strategy employing highly acidic confined iminoimidodiphosphate (iIDP) Brønsted acids 308 that catalyzed asymmetric Prins cyclizations of both aliphatic and aromatic aldehydes

An atom-economical addition of methyl azaarenes with aromatic aldehydes via benzylic C(sp³)–H bond functionalization under solvent- and catalyst-free conditions

• Divya Rohini Yennamaneni,
• Vasu Amrutham,
• Krishna Sai Gajula,
• Rammurthy Banothu,
• Murali Boosa and
• Narender Nama

Beilstein J. Org. Chem. 2020, 16, 3093–3103, doi:10.3762/bjoc.16.259

• functionalization [21][22]. The synthesis of pyridine and related azaarene derivatives involve the C(sp3)–H activation of 2-methylpyridines using different transition-metal compounds, Lewis acids, and Brønsted acids [23][24][25][26][27][28]. Recently, C(sp3)–H functionalizations of methylazaarenes with isatins and

Natural dolomitic limestone-catalyzed synthesis of benzimidazoles, dihydropyrimidinones, and highly substituted pyridines under ultrasound irradiation

• Kumar Godugu,
• Venkata Divya Sri Yadala,
• Mohammad Khaja Mohinuddin Pinjari,
• Trivikram Reddy Gundala,
• Lakshmi Reddy Sanapareddy and
• Chinna Gangi Reddy Nallagondu

Beilstein J. Org. Chem. 2020, 16, 1881–1900, doi:10.3762/bjoc.16.156

• pharmacological properties [32][33][34][35][36][37]. A wide variety of Brønsted acids and Lewis acids are employed as efficient catalysts for the Biginelli reaction [38][39][40][41][42][43][44][45][46][47]. In addition, some transition metal-based catalysts and a few nonacidic inorganic salts are also utilized as

The charge-assisted hydrogen-bonded organic framework (CAHOF) self-assembled from the conjugated acid of tetrakis(4-aminophenyl)methane and 2,6-naphthalenedisulfonate as a new class of recyclable Brønsted acid catalysts

• Svetlana A. Kuznetsova,
• Alexander S. Gak,
• Yulia V. Nelyubina,
• Vladimir A. Larionov,
• Han Li,
• Michael North,
• Vladimir P. Zhereb,
• Alexander F. Smol'yakov,
• Artem O. Dmitrienko,
• Michael G. Medvedev,
• Igor S. Gerasimov,
• Ashot S. Saghyan and
• Yuri N. Belokon

Beilstein J. Org. Chem. 2020, 16, 1124–1134, doi:10.3762/bjoc.16.99

• that are insoluble in organic solvents and derived from the neutralization of polyacidic and polybasic tectones could be good candidates for becoming efficient heterogeneous Brønsted acids. Herein, we report the synthesis of a novel, purely organic, charge-assisted hydrogen-bonded self-assembled

• applications of the material. Thus, the catalytic properties of uncrystallized F-1 and F-1 with an F-1a phase were explored in a series of reactions typically promoted by Brønsted acids, such as epoxide ring openings with methanol and water (Scheme 2). The reactions were conducted at room temperature, and

Asymmetric synthesis of CF₂-functionalized aziridines by combined strong Brønsted acid catalysis

• Xing-Fa Tan,
• Fa-Guang Zhang and
• Jun-An Ma

Beilstein J. Org. Chem. 2020, 16, 638–644, doi:10.3762/bjoc.16.60

• ; difluoromethyl compounds; fluorinated diazo reagents; strong Brønsted acids; Introduction Chiral aziridines are prevalently found in natural products and artificially made bioactive molecules, thus receiving significant attention in the past decades [1][2][3][4][5][6]. Among them, the introduction of fluorine

• no enantioselectivity at all. As arylboronic acids have been harnessed to enhance the Brønsted acidity in asymmetric organocatalysis in combination with chiral diols or chiral aminoalcohols [40][41][42][43][44], we envisioned that the simultaneous use of arylboronic acids and chiral Brønsted acids

• limited Brønsted acidity of chiral phosphoric acids. Bearing this in mind, we then turned our attention to chiral disulfonimides developed by List, which have been established as a unique type of stronger Brønsted acids [45]. Putting it into practice, a range of BINOL-derived disulfonimides was used as

Oligomeric ricinoleic acid preparation promoted by an efficient and recoverable Brønsted acidic ionic liquid

• Fei You,
• Xing He,
• Song Gao,
• Hong-Ru Li and
• Liang-Nian He

Beilstein J. Org. Chem. 2020, 16, 351–361, doi:10.3762/bjoc.16.34

• be used as catalyst in the synthesis of oligomeric ricinoleic acid, the estolide with an acid value of 48 ± 2.5 mg KOH/g was obtained after 14 h [28]. Nevertheless, the product separation and catalyst reusability have not yet been investigated until now. Based on the fact that Brønsted acids present

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• Marie Curie-Skłodowska Sq., 20-031 Lublin, Poland 10.3762/bjoc.16.11 Abstract β-Hydroxyalkylphosphine sulfides undergo [1,3]- or [1,4]-sulfur atom phosphorus-to-carbon migration in the presence of Lewis or Brønsted acids. The direction of sulfur atom migration depends on the type of acid used for the

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• difficult due to their rather nonpolar transition states, which are difficult to be addressed by catalysts [29]. Several stereoselective [3,3]-sigmatropic rearrangements are realized with chiral Brønsted acids [30][31][32][33][34]. Jacobsen reported guanidinium-catalyzed enantioselective Claisen

Friedel–Crafts approach to the one-pot synthesis of methoxy-substituted thioxanthylium salts

• Kenta Tanaka,
• Yuta Tanaka,
• Mami Kishimoto,
• Yujiro Hoshino and
• Kiyoshi Honda

Beilstein J. Org. Chem. 2019, 15, 2105–2112, doi:10.3762/bjoc.15.208

• ) sulfide (1a) with benzoyl chloride (2a) in the presence of Brønsted acids in chlorobenzene at several temperatures (Table 1). When we used a strong Brønsted acid such as trifluoromethanesulfonic acid (TfOH) at room temperature, the desired thioxanthylium salt 3a was obtained with 21% yield while other

• typical Brønsted acids did not work efficiently (Table 1, entries 1–8) [2][9][10]. At 60 °C, the yield effectively improved to 60% (Table, entry 9). Moreover, when the reaction temperature was increased to 90 °C, 120 °C, and reflux, higher yields were observed, especially under reflux conditions providing

α-Photooxygenation of chiral aldehydes with singlet oxygen

• Dominika J. Walaszek,
• Magdalena Jawiczuk,
• Jakub Durka,
• Olga Drapała and
• Dorota Gryko

Beilstein J. Org. Chem. 2019, 15, 2076–2084, doi:10.3762/bjoc.15.205

• methodologies enabling their functionalization, particularly in a stereoselective manner. Among them, asymmetric α-oxygenation of aldehydes still represents a challenging task. Most efficient methods require simultaneous use of chiral amines or Brønsted acids, and harsh oxidants like nitrosobenzene [1][2][3

Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkyl-substituted benzimidazoles with arenes in the superacid CF₃SO₃H. NMR and DFT studies of dicationic electrophilic species

• Dmitry S. Ryabukhin,
• Alexey N. Turdakov,
• Natalia S. Soldatova,
• Mikhail O. Kompanets,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1962–1973, doi:10.3762/bjoc.15.191

• –8 with arenes under the action of Brønsted acids (H2SO4, TfOH) or Lewis acids (AlX3, X = Cl, Br). Reactions of 2-formyl-1-methylbenzimidazole (1) with various arenes (benzene, and its methyl, methoxy or chloro-substituted derivatives) are given in Table 3. These reactions proceed on the formyl group

Different reactivity of phosphorylallenes under the action of Brønsted or Lewis acids: a crucial role of involvement of the P=O group in intra- or intermolecular interactions at the formation of cationic intermediates

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2019, 15, 1491–1504, doi:10.3762/bjoc.15.151

• phosphonic acids and other phosphorus-containing compounds. Contrary to Brønsted acids, 3-methylbuta-1,2-dien-1-ylphosphonic dichloride [Cl2(O=)P–HC=C=CMe2] reacted with the Lewis acid AlCl3 in an intermolecular way forming noncyclic intermediates, which were investigated by NMR spectroscopy and DFT

• electrophiles, such as sulfenyl, selenyl, and telluryl chlorides, were used in reactions with these allenes. However, only a few studies have been focused on reactions of phosphorylallenes with Brønsted acids [11][12]. These reactions proceed through an intermediate formation of the corresponding 2,5-dihydro

• phosphoryl group: chloro (1a–d), amino (1e–g), arylsulfanyl (1h,i), and methoxy (1j). Results and Discussion Reactions of allenes with Brønsted acids Allenes 1a,b,e–j upon dissolving in TfOH in an NMR tube at room temperature formed intensively colored solutions of the corresponding 1,2-oxaphospholium ions A

Robust perfluorophenylboronic acid-catalyzed stereoselective synthesis of 2,3-unsaturated O-, C-, N- and S-linked glycosides

• Madhu Babu Tatina,
• Xia Mengxin,
• Rao Peilin and
• Zaher M. A. Judeh

Beilstein J. Org. Chem. 2019, 15, 1275–1280, doi:10.3762/bjoc.15.125

• ]. The Ferrier rearrangement is one of the most useful processes to synthesize pseudo-glycosides in a direct and stereoselective fashion. Several classes of catalysts have been successfully applied in the Ferrier rearrangement including Brønsted acids [7][8][9][10][11][12][13], Lewis acids [14][15][16

Efficient synthesis of 4-substituted-ortho-phthalaldehyde analogues: toward the emergence of new building blocks

• Clémence Moitessier,
• Ahmad Rifai,
• Pierre-Edouard Danjou,
• Isabelle Mallard and
• Francine Cazier-Dennin

Beilstein J. Org. Chem. 2019, 15, 721–726, doi:10.3762/bjoc.15.67

• ) in the presence of different Brønsted acids. While investigating these conditions in combination with microwave irradiation (Scheme 4), the desired compound 4-HO-OPA (6) was successfully obtained in only 30 minutes, with a good yield (75%) when reacting with methanesulfonic acid (MsOH) as catalyst

Aqueous olefin metathesis: recent developments and applications

• Valerio Sabatino and
• Thomas R. Ward

Beilstein J. Org. Chem. 2019, 15, 445–468, doi:10.3762/bjoc.15.39

• the benzylidene moiety, such as NO2 [58], they proposed an “electron-donating to electron-withdrawing activity switch”, consisting of an in situ formation of quaternary ammonium salts by treatment with Brønsted acids (Scheme 10). Several metathesis reactions were performed in methanol/water mixtures

Syntheses and chemical properties of β-nicotinamide riboside and its analogues and derivatives

• Mikhail V. Makarov and
• Marie E. Migaud

Beilstein J. Org. Chem. 2019, 15, 401–430, doi:10.3762/bjoc.15.36

• reactivity of the 5′-OH. Modifications of the carboxyl functionality have also been explored to generate amide and ester derivatives of NR+ and nicotinic acid riboside (NAR), respectively. 3.1 Stability of NR+ to Brønsted acids and bases Unlike Nam and nicotinic acid (NA) which are chemically stable, NR

Generation of 1,2-oxathiolium ions from (arysulfonyl)- and (arylsulfinyl)allenes in Brønsted acids. NMR and DFT study of these cations and their reactions

• Stanislav V. Lozovskiy,
• Alexander Yu. Ivanov,
• Olesya V. Khoroshilova and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2018, 14, 2897–2906, doi:10.3762/bjoc.14.268

• . Petersburg State University, Universitetskiy pr., 26, Saint Petersburg, Petrodvoretz, 198504 , Russia Department of Chemistry, Saint Petersburg State Forest Technical University, Institutsky per., 5, Saint Petersburg, 194021, Russia 10.3762/bjoc.14.268 Abstract In strong Brønsted acids (CF3SO3H, FSO3H

• , the behavior of allenes 1a,b and 2a–h in Brønsted acids (TfOH, D2SO4) was studied by means of NMR (Table 1). Dissolving these allenes in TfOH or D2SO4 directly in NMR tubes at room temperature gave intensively colored red solutions of cationic species, which were stable for a long time. The NMR data

• high positive charge on it. Another pathway may be an electrophilic cyclization at the ortho-carbon in the S-phenyl ring. Then, the preparative reactions of allene 2a under the action of different electrophilic reagents were conducted. Transformations of 2a using an excess of various Brønsted acids

Cationic cobalt-catalyzed [1,3]-rearrangement of N-alkoxycarbonyloxyanilines

• Itaru Nakamura,
• Mao Owada,
• Takeru Jo and
• Masahiro Terada

Beilstein J. Org. Chem. 2018, 14, 1972–1979, doi:10.3762/bjoc.14.172

• , entry 20), the catalytic activity was diminished at 30 °C (Table 1, entry 21). Neutral CoCl2 did not promote the present reaction (Table 1, entry 22). Brønsted acids, such as trifluoromethanesulfonic acid and diphenylphosphoric acid, were much less active (Table 1, entries 23 and 24). The kind of the

β-Hydroxy sulfides and their syntheses

• Mokgethwa B. Marakalala,
• Edwin M. Mmutlane and
• Henok H. Kinfe

Beilstein J. Org. Chem. 2018, 14, 1668–1692, doi:10.3762/bjoc.14.143

• Brønsted and Lewis acid and base catalysis. Pizzo and co-workers conducted a comparative study on the catalytic activity of Lewis and Brønsted acids as well as bases for the thiolysis of epoxides using InCl3, p-TsOH, n-Bu3P and K2CO3 as representative examples, respectively. Although all of them effected

One hundred years of benzotropone chemistry

• Arif Dastan,
• Haydar Kilic and
• Nurullah Saracoglu

Beilstein J. Org. Chem. 2018, 14, 1120–1180, doi:10.3762/bjoc.14.98

• Brønsted acids (Scheme 36) [142]. Bauld and Brown reported the ready generation of the first detectable dianion radicals as outlined in Scheme 36 [150]. Benzo[7]annulenide (benzotropenide) dianion radical 220 was generated in two steps from 12 via benzotropyl methyl ether 219. Holzmann’s group described