Helicene synthesis by Brønsted acid-catalyzed cycloaromatization in HFIP [(CF₃)₂CHOH]

• Takeshi Fujita,
• Noriaki Shoji,
• Nao Yoshikawa and
• Junji Ichikawa

Beilstein J. Org. Chem. 2021, 17, 396–403, doi:10.3762/bjoc.17.35

• , and heterohelicenes. Results and Discussion Carbohelicenes such as [5]helicene (1a) and [6]helicene (1b) were synthesized via Suzuki–Miyaura coupling of readily available dihalogenated arenes 2 with phenylboronic acid ester 3 bearing a (1,3-dioxolan-2-yl)methyl group [29], followed by triflic acid

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

• ethers 41b upon the reaction in a dichloromethane solution of sulfuric acid or triflic acid [60][61]. The authors also reported that indenes 42 could undergo a subsequent Friedel–Crafts alkylation when 41b was reacted in the presence of an external aromatic partner Ar’H in pure triflic acid. Thus, a

• carbenium ions have also been suggested to exist as reaction intermediates. During their investigations on the reactivity of sulfuranes under acidic conditions, Martin et al. reported that sulfurane 44 reacts with triflic acid to provide alcohol 9g and sultine 46, according to 1H and 19F NMR assignments

• much faster than that of 45f by at least a factor of 10, encouraging the authors to suggest “a transition state resembling 48f in the rate-limiting step”. Sulfurane 53, bearing OC(CF3)3 groups, was also treated with triflic acid, affording dialkylsulfonium species 54 in 91% yield along with perfluoro

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• -benzoyl-2,2-difluoro-3-phenylcyclopropane and its derivatives into 3-fluoro-2,5-diphenylfuran derivatives following the brief exposure to triflic acid (2 equiv) in cold dichloromethane [100]. Dolbier et al. described the ring opening of 2,2-difluorocyclopropyl ketones 113 (Scheme 51) [101]. The reactions

• -fluoropyrroles 142 (Scheme 62) [113]. The reaction involved the gem-difluorocyclopropyl ketones 143 and nitriles 144. It was proposed that the protonation of the ketone with triflic acid led to a partial ring opening of the gem-difluorocyclopropyl ketone to generate a carbocation-like center that was stabilized

Synthesis, crystal structures and properties of carbazole-based [6]helicenes fused with an azine ring

• Daria I. Tonkoglazova,
• Anna V. Gulevskaya,
• Konstantin A. Chistyakov and
• Olga I. Askalepova

Beilstein J. Org. Chem. 2021, 17, 11–21, doi:10.3762/bjoc.17.2

• delight, treating 9a and 9b with triflic acid in СH2Cl2 solution at room temperature allowed us to obtain helicenes 10a and 10b in high yields (Table 5, entries 1 and 2). Apparently, the presence of the aza group adjacent to the triple bond in compounds 9a and 9b causes the observed difference in the

Pentannulation of N-heterocycles by a tandem gold-catalyzed [3,3]-rearrangement/Nazarov reaction of propargyl ester derivatives: a computational study on the crucial role of the nitrogen atom

• Giovanna Zanella,
• Martina Petrović,
• Dina Scarpi,
• Ernesto G. Occhiato and
• Enrique Gómez-Bengoa

Beilstein J. Org. Chem. 2020, 16, 3059–3068, doi:10.3762/bjoc.16.255

• anion as a base (Figure 6). In fact, the abstraction of the hydrogen atom in the position adjacent to Au (C3) shows a low activation barrier (TS8, ΔG‡ = 12.6 kcal⋅mol−1) from the corresponding precomplex, leading to the formation of the intermediate XI and triflic acid. The high acidity of the latter

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• monoformylsumanene 66 and monoacetylsumanene 69 in good yields. The monobenzoylsumanene 81 was prepared from benzoyl chloride in the presence of triflic acid. Moreover, disubstituted sumanene derivatives 83–85 were prepared under similar reaction conditions just by increasing the amount of the reagents and easily

• yield. Next, compound 202 was treated with KI/NaNO2 under Sandmeyer reaction conditions to afford the triiodo compound 203 which on subsequent reaction with mCPBA and triflic acid (TfOH) provided the iodine-doped sumanene 204 in 68% yield. Finally, compound 204 was converted to the required

Synthesis of monophosphorylated lipid A precursors using 2-naphthylmethyl ether as a protecting group

• Jundi Xue,
• Ziyi Han,
• Gen Li,
• Khalisha A. Emmanuel,
• Cynthia L. McManus,
• Qiang Sui,
• Dongmian Ge,
• Qi Gao and
• Li Cai

Beilstein J. Org. Chem. 2020, 16, 1955–1962, doi:10.3762/bjoc.16.162

• , followed by deprotection, acylation, and phosphorylation reactions (Scheme 4). The triflic acid (TfOH)-mediated glycosylation of donor 20 and acceptor 18 in the presence of molecular sieves in CH2Cl2 at −20 °C gave disaccharide 24 [14] in excellent yield (β-anomer only). The N’-Troc protecting group (non

One-pot synthesis of isosorbide from cellulose or lignocellulosic biomass: a challenge?

• Isaline Bonnin,
• Raphaël Mereau,
• Thierry Tassaing and
• Karine De Oliveira Vigier

Beilstein J. Org. Chem. 2020, 16, 1713–1721, doi:10.3762/bjoc.16.143

• hydrolysis of cellulose and dehydration of sorbitol and sorbitans was studied and their efficiency decreased in the order of H2SO4 > triflic acid (HOTf) > trifluoroacetic acid (TFA) > Amberlyst-38 > HCl > HNO3. It was shown that when MCC was used as starting material, in the presence of Ru/C and H2SO4, 50

Copper-catalyzed O-alkenylation of phosphonates

• Nuria Vázquez-Galiñanes,
• Mariña Andón-Rodríguez,
• Patricia Gómez-Roibás and
• Martín Fañanás-Mastral

Beilstein J. Org. Chem. 2020, 16, 611–615, doi:10.3762/bjoc.16.56

• triflic acid via decomposition of ethyl triflate. As a limitation, substrates bearing a vinyl substituent or an enolizable ester group did not give any conversion. This methodology is also applicable to other dialkyl phosphonates as illustrated by the synthesis of enol phosphonates 3j, 3k and 3l

SnCl₄-catalyzed solvent-free acetolysis of 2,7-anhydrosialic acid derivatives

• Kesatebrhan Haile Asressu and
• Cheng-Chung Wang

Beilstein J. Org. Chem. 2019, 15, 2990–2999, doi:10.3762/bjoc.15.295

• can be transformed smoothly into thioglycoside [15][16][35] and sialyl halide [38][39] donors when treated with a thiol in the presence of triflic acid, BF3⋅OEt2, and HCl, respectively. Through comparison with the reported mechanism of Sc(OTf)3-catalyzed acetolysis of 1,6-anhydro-β-hexopyranoses [32

Effect of ring size on photoisomerization properties of stiff stilbene macrocycles

• Sandra Olsson,
• Óscar Benito Pérez,
• Magnus Blom and
• Adolf Gogoll

Beilstein J. Org. Chem. 2019, 15, 2408–2418, doi:10.3762/bjoc.15.233

• an example. Numbering of carbons in compounds (Z)-1a–d, showing (Z)-1d as an example. The stiff stilbene photoisomerization from Z to E and vice versa by irradiation at 300 nm and 360 nm, respectively. Synthetic route to SS-macrocycles. i. (1) Triflic acid (3 equiv), DCM (dry), Ar atmosphere, MW (110

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

• –Crafts reaction; triflic acid; Introduction Imidazoles and benzimidazoles are important heterocyclic scaffolds in pharmaceuticals and agrochemicals [1][2][3][4][5][6][7][8][9][10]. They also have applications in the fields of dyes, chemo-sensing, and fluorescent materials [3]. (Benz)imidazoles are a

• , superelectrophilic activation of the carbonyl group was achieved for 5-formyl and 5-acetylimidazoles in triflic acid CF3SO3H (TfOH) by Klumpp [19]. It was proposed that the triflic acid initially protonated the imidazole ring and an equilibrium was established with the O-protosolvated form or the dicationic

• (Figure 3) with arenes under the action of Brønsted (super)acids CF3SO3H (TfOH, triflic acid), H2SO4 and strong Lewis acids AlX3 (X = Cl, Br). One would expect the electrophilic activation of carbonyl or 2-hydroxyalkyl groups of these benzimidazoles in hydroxyalkylation and alkylation of arenes. Results

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• ]. The reaction was initially tried with different catalysts like triflic acid, I2, salts of Pd, Fe, Co and Cu which did not lead to the formation of the final product except CuSO4 and CuCl2 which gave a moderate yield of the products. Further studies revealed CuBr to be the most effective with a maximum

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

• benzaldehyde. A nickel-catalyzed procedure gives the dipyridyl intermediate 7 [13]. This is easily oxidized to the diketone 8 and reaction of this substance with 2-lithiopyridine gives the precursor 9. The diol 9 is a substrate with six ionizable groups. Upon ionization in superacidic CF3SO3H (triflic acid

• performed using oven-dried glassware under an argon atmosphere. Trifluoromethanesulfonic acid (triflic acid) was freshly distilled prior to use. All commercially available compounds and solvents were used as received. 1H and 13C NMR were done using either 300 MHz or 500 MHz spectrometer; chemical shifts

• °C, compound 9 (52.2 mg, 0.10 mmol) was dissolved in benzene (1 mL, 11.2 mmol), stirred for 5 min before triflic acid (1 mL, 11 mmol) was slowly added and the tube was then tightly closed. Following 24 h of stirring at 60–70 °C, the reaction was cooled to room temperature, poured on about 10 g of ice

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

• ; oxaphospholium ions; phosphorylallenes; phosphoryl group; triflic acid; Introduction Electrophilic reactions of allenes have been intensely explored in organic synthesis [1][2][3]. In particular, reports on electrophilic activation of phosphorylallenes are numerous [4][5][6][7][8][9][10]. Miscellaneous

A three-component, Zn(OTf)₂-mediated entry into trisubstituted 2-aminoimidazoles

• Alexei Lukin,
• Anna Bakholdina,
• Anna Kryukova,
• Alexander Sapegin and
• Mikhail Krasavin

Beilstein J. Org. Chem. 2019, 15, 1061–1064, doi:10.3762/bjoc.15.103

• %). Notably, neither Sc(OTf)2 nor Cu(OTf)2 employed as catalysts produced a trace of the desired product. To rule out catalysis by adventitious TfOH, the reaction was performed in the presence of an equimolar amount of triflic acid, but no conversion could be detected (Table 1). Considering that in situ

A pyridinium/anilinium [2]catenane that operates as an acid–base driven optical switch

• Sarah J. Vella and
• Stephen J. Loeb

Beilstein J. Org. Chem. 2018, 14, 1908–1916, doi:10.3762/bjoc.14.165

• easily understood as the neutral benzylaniline site does not allow for appreciable non-covalent interactions and cannot compete for the DB24C8 ring with the dicationic bis(pyridinium)ethane site. However, the addition of one equivalent of triflic acid (CF3SO3H) to a solution of [8DB24C8]6+ results in

Synthesis of new tricyclic 5,6-dihydro-4H-benzo[b][1,2,4]triazolo[1,5-d][1,4]diazepine derivatives by [3⁺ + 2]-cycloaddition/rearrangement reactions

• Lin-bo Luan,
• Zi-jie Song,
• Zhi-ming Li and
• Quan-rui Wang

Beilstein J. Org. Chem. 2018, 14, 1826–1833, doi:10.3762/bjoc.14.155

• illustrated in Scheme 1, the preparation starts from the related anilines 1 which were acylated with 3-bromopropionyl chloride (2) to afford amides 3. Upon basic treatment with t-BuONa, the amides 3 were converted to the cyclized β-propiolactams 4. In the presence of triflic acid, the Fries rearrangement

Recent advances in hypervalent iodine(III)-catalyzed functionalization of alkenes

• Xiang Li,
• Pinhong Chen and
• Guosheng Liu

Beilstein J. Org. Chem. 2018, 14, 1813–1825, doi:10.3762/bjoc.14.154

• environment at the iodine center. Mechanistically, the iodine(III) 16 is activated by triflic acid generating a free coordination site at the iodine(III) center [54]. The coordination of the alkene to the activated iodine(III) center generates the required prochiral face differentiation and the nucleophilic

Synthesis and stability of strongly acidic benzamide derivatives

• Frederik Diness,
• Niels J. Bjerrum and
• Mikael Begtrup

Beilstein J. Org. Chem. 2018, 14, 523–530, doi:10.3762/bjoc.14.38

• enable their incorporation into functional materials (e.g., polymers), these acids need additional functionality in the form of a reactive group, and the chemistry applied for functionalization must be compatible with their strong acidic nature. Many types of strong organic acids such as triflic acid (7

Aminosugar-based immunomodulator lipid A: synthetic approaches

• Alla Zamyatina

Beilstein J. Org. Chem. 2018, 14, 25–53, doi:10.3762/bjoc.14.3

• deprotected by treatment with tetrabutylammonium fluoride buffered with acetic acid, and the resulting lactol was converted to the imidate donor 11 which was coupled to the orthogonally protected acceptor, an azide 12, using triflic acid as promotor (Scheme 2). Subsequent hydrolytic cleavage of the

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

Intramolecular glycosylation

• Xiao G. Jia and
• Alexei V. Demchenko

Beilstein J. Org. Chem. 2017, 13, 2028–2048, doi:10.3762/bjoc.13.201

• alcohol showed good selectivity (α/β = 4.8:1) when boronic acid and NBS were employed. Control experiments with a thiophenyl or a thiobenzyl leaving group showed lower stereoselectivities and a slight reduction in yields. The addition of triflic acid or silver triflate resulted in a significant reduction

1,3-Dibromo-5,5-dimethylhydantoin as promoter for glycosylations using thioglycosides

• Fei-Fei Xu,
• Claney L. Pereira and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2017, 13, 1994–1998, doi:10.3762/bjoc.13.195

• GmbH, Magnusstraße 11, 12489 Berlin, Germany 10.3762/bjoc.13.195 Abstract 1,3-Dibromo-5,5-dimethylhydantoin (DBDMH), an inexpensive, non-toxic and stable reagent, is a competent activator of thioglycosides for glycosidic bond formation. Excellent yields were obtained when triflic acid (TfOH) or

Synthesis of alkynyl-substituted camphor derivatives and their use in the preparation of paclitaxel-related compounds

• M. Fernanda N. N. Carvalho,
• Rudolf Herrmann and
• Gabriele Wagner

Beilstein J. Org. Chem. 2017, 13, 1230–1238, doi:10.3762/bjoc.13.122

• /13C NMR experiments, and by comparison with relatively similar compounds obtained in the reaction of the bis(phenylalkynyl)-derivative of 4a with triflic acid [26], or with K[ReO4] [27]. The polycyclic carbon skeleton in these is identical, but the latter compounds are protonated at the sulfonimide