Cyclization of 1-aryl-4,4,4-trichlorobut-2-en-1-ones into 3-trichloromethylindan-1-ones in triflic acid

• Vladislav A. Sokolov,
• Andrei A. Golushko,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2023, 19, 1460–1470, doi:10.3762/bjoc.19.105

• -enones) undergo intramolecular transformation into 3-trichloromethylindan-1-ones (CCl3-indanones) in Brønsted superacid CF3SO3H (triflic acid, TfOH) at 80 °C within 2–10 h in yields up to 92%. Protonation of the carbonyl oxygen of the starting CCl3-enones by TfOH affords the key reactive intermediates

• =CHC(=O)Me] with arenes in Brønsted superacid TfOH (triflic acid, CF3SO3H) furnishes 3-methyl-1-trichloromethylindenes (Scheme 1a) [11]. Based on NMR analysis in TfOH and theoretical DFT calculations, it has been found that the reaction proceeds through an intermediate formation of the O-protonated

• ., under conditions of incomplete conversion of the starting compounds. It was found that, apart from the target indanones 3, substantial amounts of the corresponding enones 2 were detected (Table 1). This means that, in the superacid TfOH, hydroxy ketones 1 may initially undergo dehydration to enones 2

On drug discovery against infectious diseases and academic medicinal chemistry contributions

• Yves L. Janin

Beilstein J. Org. Chem. 2022, 18, 1355–1378, doi:10.3762/bjoc.18.141

• [288][289][290][291][292][293]. Moreover, the use/design of new chemical reactions may lead to hard-to-get and original analogues possibly better than the one reported. One example, depicted in Scheme 2, would be the fluorination, under superacid conditions [294], of the highly elaborated anticancer

AlBr₃-Promoted stereoselective anti-hydroarylation of the acetylene bond in 3-arylpropynenitriles by electron-rich arenes: synthesis of 3,3-diarylpropenenitriles

• Yelizaveta Gorbunova,
• Dmitry S. Ryabukhin and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2663–2667, doi:10.3762/bjoc.17.180

• ]. Recently, we have shown that reactions of 3-arylpropenenitriles (cinnamonitriles, ArCH=CHCN) with arenes (Ar′H) under the superelectrophilic activation by the Brønsted superacid CF3SO3H (TfOH, triflic acid) or the strong Lewis acid AlBr3 result in the formation of 3,3-diarylpropanenitriles (Ar(Ar′)CHCH2CN

• arenes under the action of the strong Lewis acids, aluminum halogenides AlX3 (X = Cl, Br) and the Brønsted superacid TfOH (CF3SO3H). Results and Discussion It was found that acetylene nitriles 1a–c reacted with arenes in the presence of excess AlBr3 (6 equiv) at room temperature for 0.5–2 h to afford E,Z

Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

• Andrey I. Puzanov,
• Dmitry S. Ryabukhin,
• Anna S. Zalivatskaya,
• Dmitriy N. Zakusilo,
• Darya S. Mikson,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2021, 17, 2417–2424, doi:10.3762/bjoc.17.158

• the transformations of these heterocyclic compounds in electrophilic media. The main goals of this work were the synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and the study of their reactions with/without arenes under the conditions of superelectrophilic activation by the Brønsted superacid CF3SO3H

• ). Conclusion For the first time reported, we have synthesized 5-arylacetylene derivatives of 1,2,4-oxadiazoles, i.e., 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles. In the Brønsted superacid TfOH, these oxadiazoles react in a way of electrophilic addition to the acetylene bond. They give products of

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

• of xanthenes and thioxanthenes by intramolecular FCA catalyzed with organic Brønsted superacid, which are our works [41][42]. According to the literature, there are also hydroarylation methods with FCA, which are made by unactivated alkenes instead of π-activated alcohols. In these studies, generally

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

•  18). A sequence of reactions involving elimination of a proton from 83, treatment of 84 with an alkoxide, and protonation of the resulting enolate delivered thermodynamically favored equatorial ester 80 and 81. The highly diastereoselective Brønsted superacid-catalyzed Prins cyclization of

CF₃-substituted carbocations: underexploited intermediates with great potential in modern synthetic chemistry

• Anthony J. Fernandes,
• Armen Panossian,
• Bastien Michelet,
• Agnès Martin-Mingot,
• Frédéric R. Leroux and
• Sébastien Thibaudeau

Beilstein J. Org. Chem. 2021, 17, 343–378, doi:10.3762/bjoc.17.32

• absent or upon installation of an additional CF3 group, only the corresponding protonated alcohols 10d–g were observed. Olah et al. also reported the 13C NMR chemical shifts for carbenium ion 10c upon ionization of the alcohol precursor 9c in a superacid (Scheme 4) [36]. A large downfield shift was

• , Vasilyev and Khoroshilova investigated the superacid-promoted activation of α-(trifluoromethyl) silyl ethers exhibiting a thiophene core [73]. At 0 °C, thiophenes 72-Cl and 72-Br undergo electrophilic dimerization, affording a mixture of 73-Cl and 73-Br (Scheme 20). When the reaction was cooled to −60 °C

• a superacid [78]. When allylic alcohol 99 was ionized with SbF5 in SO2ClF at −78 °C, the corresponding α-(trifluoromethyl)allylcarbenium ion 100 was formed. The carbons atoms C1 and C2 exhibited very different chemical shifts, δC1 = 157 ppm and δC2 = 290 ppm, which are to be compared to the

A new method for the synthesis of diamantane by hydroisomerization of binor-S on treatment with sulfuric acid

• Rishat I. Aminov and
• Ravil I. Khusnutdinov

Beilstein J. Org. Chem. 2020, 16, 2534–2539, doi:10.3762/bjoc.16.205

• , PtO2) in glacial acetic acid under high pressure conditions at 70 °С and 200 psi of H2 [8][9]. In the presence of superacid catalysts, such as B(OSO2CF3)3, CF3SO3H/SbF5 1:1, CF3SO3H/B(OSO2CF3)3 1:1 [10], NaBH4/CF3SO3H [11], or zeolite Y in the NaH form (NaY) [12], hydrocarbons 3a–c isomerize to

Reactions of 3-aryl-1-(trifluoromethyl)prop-2-yn-1-iminium salts with 1,3-dienes and styrenes

• Thomas Schneider,
• Michael Keim,
• Bianca Seitz and
• Gerhard Maas

Beilstein J. Org. Chem. 2020, 16, 2064–2072, doi:10.3762/bjoc.16.173

• -substituted iminium groups with electron-rich (hetero)aromatics are known [18][24]. Furthermore, 1-(trifluoromethyl)indenes have recently been generated by cationic cyclization of β-aryl trifluoromethyl enones under superacid conditions [42][43][44]. Styrenes are also known to behave as dienes in [4 + 2

Direct borylation of terrylene and quaterrylene

• Haruka Kano,
• Keiji Uehara,
• Kyohei Matsuo,
• Hironobu Hayashi,
• Hiroko Yamada and
• Naoki Aratani

Beilstein J. Org. Chem. 2020, 16, 621–627, doi:10.3762/bjoc.16.58

• with AlCl3 reproducibly provided a pure terrylene [8]. Scholl reaction using a superacid catalyst in combination with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant provides a scalable preparation of quaterrylene [9], but unfortunately the low solubility prevents 1H NMR characterization

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• . This supports thermodynamic control based on carbocation energies. Keywords: arenium ion; carbocation; density functional theory; microwave reaction; rearrangement; superacid; Introduction Carbocations are enigmatic reactive intermediates of enduring importance in chemistry. No other reactive species

• displays such a complex and fascinating collection of molecular rearrangements. Building on a long history, new synthetic applications [1][2] and explanations of carbocation reaction mechanisms [3][4][5][6] continue to be discovered. Chemistry in superacid solutions has played a major role in this field [7

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

• nab., 7/9, Saint Petersburg, 199034, Russian Federation 10.3762/bjoc.15.191 Abstract Reactions of 2-carbonyl- and 2-hydroxy(or methoxy)alkylbenzimidazoles with arenes in the Brønsted superacid TfOH resulted in the formation of the corresponding Friedel–Crafts reaction products, 2-diarylmethyl and 2

• superacids or coordination by a Lewis superacid to produce a di- (tri- or higher) cationic species, the study of superelectrophilic activation became a very active area of research [11][12][13]. The acid-catalyzed condensation of ketones and aldehydes with aromatic compounds is known as the hydroxyalkylation

• benzimidazole system. The same applies to the reactivity of the carbon C2 in dications I and II. Then we studied the protonation of benzimidazoles in the superacid TfOH by means of NMR. Selected 1H, 13C and 15N NMR data for starting neutral benzimidazoles 1, 3a, and 7 (in CDCl3, (CD3)2CO, CD3OD) and their

Superelectrophilic carbocations: preparation and reactions of a substrate with six ionizable groups

• Sean H. Kennedy,
• Makafui Gasonoo and
• Douglas A. Klumpp

Beilstein J. Org. Chem. 2019, 15, 1515–1520, doi:10.3762/bjoc.15.153

• in the Brønsted superacid CF3SO3H, the substrate undergoes two types of reactions. In the presence of only the superacid, the highly ionized intermediate(s) provide a double cyclization product having two pyrido[1,2-a]indole rings. With added benzene, an arylation product is obtained. A mechanism is

• proposed involving tetra-, penta-, or hexacationic species. Keywords: cation; Friedel–Crafts; heterocycle; superacid; superelectrophile; Introduction During the 1970s and 80s, Olah and co-workers described the novel chemistry of highly-charged organic cationic species. This work lead to the concept of

• studies of tri-, tetra-, and pentacationic systems [11][12]. This product, 10, is the result of charge migration involving the carbocation center and the phenyl group (vide infra). When compound 9 is treated with only superacid, the bis(pyrido[1,2-a]indole) 11 is formed as the major product. Likewise, the

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

• =)P–CR=C=CMe2, X = Cl, OMe, NR2, or SAr] undergo intramolecular cyclization into the corresponding 1,2-oxaphospholium ions in the Brønsted superacid TfOH. These cations have been thoroughly studied by means of NMR spectroscopy. The hydrolysis of superacidic solutions of these species afforded cyclic

• (Figure 3, Table 2). Despite solvation in the Brønsted superacid TfOH, the P=O group takes part in intramolecular cyclization into oxaphospholium ions (Table 1). These two different types of reaction intermediates, generated from such allenes in Brønsted and Lewis acids, lead to various reaction products

• reaction mixture. An alternative pathway for species 18 is cyclization into indane structure 20, which is further transformed into 21 and 12. At the same time, an alternative mechanism B, involving the formation of the protic superacid HCl–AlCl3 and its participation in the observed reaction should be

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

• correlations, that there was a [6,7]-shift of the methyl group in the thiochromene system of 5b obtained from allene 2c, which, at first, should give 6-methyl substituted thiochromene. This shift is caused by the action of superacid at high reaction temperature. Phenyl-substituted allenes 2e,f did not afford

• to alcohols 7a,b. Conclusion Transformations of (arylsulfonyl)- and (arylsulfinyl)allenes under the action of the Brønsted superacid TfOH, or strong Lewis acids AlX3 (X = Cl, Br) have been studied. Under electrophilic conditions, these allenes form the corresponding 1,2-oxathiolium ions, which have

Strategies toward protecting group-free glycosylation through selective activation of the anomeric center

• A. Michael Downey and
• Michal Hocek

Beilstein J. Org. Chem. 2017, 13, 1239–1279, doi:10.3762/bjoc.13.123

• very common and well-studied. Typical Lewis acids employed for anomeric activation are TMSOTf and BF3·Et2O (Scheme 14). The reactions proceed through an oxocarbenium ion that was very recently observed by NMR under cryogenic (−40 °C) conditions stabilized by the HF/SbF5 superacid [52]. The highly

Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

• Anna S. Zalivatskaya,
• Dmitry S. Ryabukhin,
• Marina V. Tarasenko,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya,
• Elena V. Grinenko,
• Ludmila V. Osetrova,
• Eugeniy R. Kofanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89

• -substituted 1,2,4-oxadiazoles, is the N4,C-diprotonated species D from both the thermodynamic and electronic point of view. Next, we carried out an NMR study of the protonation of oxadiazoles 1a and 1m in the superacid FSO3H at low temperature (−80 °C). The spectra are shown in Supporting Information File 1

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

• Dmitry S. Ryabukhin,
• Dmitry N. Zakusilo,
• Mikhail O. Kompanets,
• Anton A.Tarakanov,
• Irina A. Boyarskaya,
• Tatiana O. Artamonova,
• Mikhail A. Khohodorkovskiy,
• Iosyp O. Opeida and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 2125–2135, doi:10.3762/bjoc.12.202

• part in electrophilic reactions. To investigate this issue in more detail we studied the protonation of furans 1a and 2 in the superacid TfOH by NMR spectroscopy. Upon dissolving 1a and 2 in TfOH in the NMR tube the formation of deep-red solutions was observed. 1H and 13C NMR data of the generated

• proton exchange with the superacidic medium at room temperature. Thus, the NMR data revealed that protonation of furans 1a and 2 in superacid TfOH resulted in the formation of dications A and D, respectively, although DFT calculations (Table 1) did not manifest that clearly. Next, 5-HMF (1a), 5

• formation of 5-diarylmethylfurfurals 5a–g (Table 5, Figure 2). Contrary to compound 1a, which was activated with the Brønsted superacid TfOH to achieve Friedel–Crafts products 3 and 4 (Table 3 and Table 4), compound 2 gave better results with strong Lewis acids AlX3 (X = Cl, Br) (Table 5, entries 4, 5, 9

Reactions of N,3-diarylpropiolamides with arenes under superelectrophilic activation: synthesis of 4,4-diaryl-3,4-dihydroquinolin-2(1H)-ones and their derivatives

• Larisa Yu. Gurskaya,
• Diana S. Belyanskaya,
• Dmitry S. Ryabukhin,
• Denis I. Nilov,
• Irina A. Boyarskaya and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2016, 12, 950–956, doi:10.3762/bjoc.12.93

• )-ones [12][13]. The main goal of this work was a systematic study on reactions of 3-aryl-N-(aryl)propiolamides with arenes under the action of the Brønsted superacid TfOH (CF3SO3H, triflic acid), strong Lewis acids AlX3 (X = Cl, Br), or the conjugate Brønsted–Lewis superacid TfOH–SbF5. Results and

Tricyclic flavonoids with 1,3-dithiolium substructure

• Lucian G. Bahrin,
• Peter G. Jones and
• Henning Hopf

Beilstein J. Org. Chem. 2012, 8, 1999–2003, doi:10.3762/bjoc.8.226

• survey revealed that a P2O5/CH3SO3H (1:10, m/v) mixture may be the cyclization agent of choice to obtain 1,3-dithiolium salts 7g and 7h as pure compounds and in high yields [28][29]. Thus, a suspension of 6g or 6h in three parts of the ‘‘superacid’’ mixture was stirred at room temperature for 30 min to

Molecular rearrangements of superelectrophiles

• Douglas A. Klumpp

Beilstein J. Org. Chem. 2011, 7, 346–363, doi:10.3762/bjoc.7.45

• steps similar to monocationic rearrangements, such as alkyl group shifts, Wagner–Meerwein shifts, hydride shifts, ring opening reactions, and other skeletal rearrangements. This review will describe these types of superelectrophilic reactions. Keywords: dication; rearrangement; superacid

• -(diphenylmethylene)isobenzofuranone (30). If product 29 is isolated and then treated with superacid, 30 is obtained as the sole reaction product. A mechanism for this conversion is proposed which involves the formation of the O,O-diprotonated superelectrophile 32 with subsequent ring opening and closing reaction

• which is a stable species at –80 °C [19]. Warming the solution leads to an equilibration between acylium–carboxonium dications and the bis-carboxonium dication. A similar degenerate rearrangement has also been described for glutaric anhydride in superacid. Phthalic acid (36) also undergoes a dicationic