The synthesis of chiral β-naphthyl-β-sulfanyl ketones via enantioselective sulfa-Michael reaction in the presence of a bifunctional cinchona/sulfonamide organocatalyst

• Deniz Tözendemir and
• Cihangir Tanyeli

Beilstein J. Org. Chem. 2021, 17, 494–503, doi:10.3762/bjoc.17.43

• transition state model to explain the origin of the stereoinduction was proposed (Scheme 2), according to the Houk’s Brønsted acid hydrogen bonding model. Guo’s computational work in 2017 on the sulfa-Michael addition of thiols to enones in the presence of cinchona alkaloid-type organocatalysts showed that

• while the deprotonated nucleophile is oriented by the Brønsted acid moiety. The substrate scope was extended to substituted chalcones, under the optimized conditions (Table 3). The chalcone derivatives used in this work were obtained by Claisen–Schmidt condensation, using known procedures [44]. Among

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

• metal catalysts. Recently, we have developed a Brønsted acid-catalyzed cycloaromatization in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) as solvent [20][21][22]. Fluoroalcohols, such as HFIP, exhibit high ionization power and low nucleophilicity, based on the electron-withdrawing inductive effect of

• silica gel column chromatography (hexane/CH2Cl2 = 3:1) gave 1b (1.31 g, 88%). Conventional methods for the synthesis of helicenes. Brønsted acid-catalyzed cycloaromatization of biaryls bearing an acetal moiety. Two strategies for the helicene synthesis via Suzuki–Miyaura coupling/cycloaromatization

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

• progressive conversion of the starting material into the C6-derivative 64 (Scheme 18). Chen et al. reported the synthesis of C2-phosphorylated indoles via 1,2-phosphorylation of 3-indolylmethanols with H-phosphine oxides or H-phosphonates under Brønsted acid activation [72]. The scope of the reaction includes

• a longer reaction time, allenes 127 undergo a subsequent intramolecular hydroarylation reaction leading to indenes 128. The authors suggested the formation of FeCl3–HFIP complexes being involved in a Lewis acid-assisted Brønsted acid catalysis. The CF3-substituted propargyl alcohol 129 was found to

• generate CF3-substituted iminium ions able to promote Friedel–Crafts alkylations [110][111]. Ma et al. exploited this mode of activation in a Brønsted acid-catalyzed three-component asymmetric reaction [112]. Mixing hemiacetal 175, arylaniline 176, and indole derivatives 149 in the presence of a catalytic

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity – more diversity

• Dmitrii A. Shabalin,
• Evgeniya E. Ivanova,
• Igor A. Ushakov,
• Elena Yu. Schmidt and
• Boris A. Trofimov

Beilstein J. Org. Chem. 2021, 17, 319–324, doi:10.3762/bjoc.17.29

• , namely a Brønsted acid-activated hydroxypyrroline, depend on the reaction conditions and the structure of the hydrazides. Keywords: hydrazides; pyridazines; pyrrolines; recyclization; ring expansion; Introduction Di- and tetrahydropyridazines are valuable heterocyclic motifs which are utilized as key

• saturated pyridazine scaffolds is both highly topical and necessary. Recently, we have developed a convenient approach to the 1,4-dihydropyridazine core based on the Brønsted acid-catalyzed regioselective recyclization of 5-hydroxypyrrolines (assembled in a one-pot manner from ketoximes and acetylene gas [8

Three-component reactions of aromatic amines, 1,3-dicarbonyl compounds, and α-bromoacetaldehyde acetal to access N-(hetero)aryl-4,5-unsubstituted pyrroles

• Wenbo Huang,
• Kaimei Wang,
• Ping Liu,
• Minghao Li,
• Shaoyong Ke and
• Yanlong Gu

Beilstein J. Org. Chem. 2020, 16, 2920–2928, doi:10.3762/bjoc.16.241

• obtained with AlCl3 (Table 1, entries 4 and 5). p-Toluenesulfonic acid (PTSA), a strong Brønsted acid, also exhibited a promising catalytic ability, and the yield of 4a reached 73% (Table 1, entry 6). When HOAc was used, only unreacted starting materials were recovered (Table, entry 7). The effect of the

Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• there is much progress yet to be made. Brønsted acid catalysis Using chiral amines and NHCs as catalysts to generate asymmetry relies upon the formation of covalently bonded intermediates such as enamines, iminium ions or Breslow intermediates within the catalytic cycle. The first example of merging non

• "Brønsted acid catalysis", yet interestingly their conjugate bases can also be used as efficient hydrogen bonding catalysts. Knowles et al. showed that a tricatalytic system using chiral phosphate 235 can mediate the deracemisation of cyclic urea rac-236 (Scheme 36) [97]. The proposed mechanism involves a

Fluorohydration of alkynes via I(I)/I(III) catalysis

• Jessica Neufeld,
• Constantin G. Daniliuc and
• Ryan Gilmour

Beilstein J. Org. Chem. 2020, 16, 1627–1635, doi:10.3762/bjoc.16.135

• -TolIF2 17 demonstrated the importance of the exogenous amine·HF as a Brønsted acid activator (Figure 3C). Similar yields were observed when comparing the stoichiometric reaction and the catalytic process using an amine/HF ratio of 1:7.5. To interrogate the importance of the benzoate group in the

• -fluoroketone motif from alkynes. Selectfluor®-mediated oxidation of p-TolI in the presence of an amine/HF source, which plays a dual function as fluoride source and Brønsted acid activator, enables in situ generation of p-TolIF2 (Figure 5). From these preliminary mechanistic investigations, conclusions

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

• and heterogeneous Brønsted acid catalyst, which are both required for independent steps in the synthesis [132]. They suggested that the porphyrin was protonated by the amberlyst-15 sulphonate groups and immobilised to the solid surface by electrostatic forces, rationalising the observed change in

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

• , elemental analysis, and 1H NMR spectroscopy. The framework was supported by hydrogen bonds between the sulfonate anions and the ammonium cations of NDS and protonated TAPM moieties, respectively. The CAHOF material functioned as a new type of catalytically active Brønsted acid in a series of reactions

• , providing some dissolved F-1 as the real catalyst. In all cases, the catalyst could easily be recovered and recycled. Keywords: Brønsted acid catalyst; charge-assisted hydrogen-bonded framework; Diels–Alder; epoxide ring opening; heterogeneous catalyst; Introduction Tremendous successes in homogeneous

• catalyst for the Brønsted acid-catalyzed ring opening reactions of epoxides with alcohols and water, with the latter reaction occurring in a three-phase medium. In addition, a Diels–Alder reaction was promoted by F-1 in heptane. Results and Discussion Mixing together aqueous solutions of two equivalents of

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

• combined strong Brønsted acid catalytic platform consisting of a chiral disulfonimide and 2-carboxyphenylboronic acid. The optical purity of the obtained CF2-substituted aziridines could be further improved by a practical dissolution–filtration procedure. Keywords: aziridines; chiral disulfonimides

• hinges upon the discovery of a combined strong Brønsted acid system comprised of a chiral disulfonimide and 2-carboxyphenylboronic acid. Results and Discussion We commenced the desired one-pot transformation by conducting the model reaction between phenylglyoxal monohydrate (1a), 4-methoxyaniline (2a

• phenyl sulfone under mild conditions by a combined strong Brønsted acid system consisting of chiral disulfonimide and 2-carboxyphenylboronic acid. The optical purity of the obtained CF2-substituted aziridines could be further improved by a practical dissolution–filtration procedure. Substrate expansion

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• from the oxidation of the amine with the formed [Cu(II)] complex, followed by a deprotonation by DABCO. The resulting alkoxide is finally converted into the alcohol by the protonated DABCO. During this study, the authors found that replacement of the base by the Brønsted acid (R)-1,1-binaphtyl-2,2-diyl

• avoided the presence of a Brønsted acid in the reaction media. As such, Collins and co-workers developed the catalyst [Cu(I)(pypzs)(BINAP)]BF4 where the ligand (5-(4-fluorosulfonyl)amino-3-(2pyridyl)pyrazole)) (pypzs) had an acidic proton prone to activate the carbonyl group during the pinacol coupling

Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst

• Abhijit Paul,
• Debnath Chatterjee,
• Srirupa Banerjee and
• Somnath Yadav

Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16

• oxidative dehydrogenation [19]. Recently, Maji and co-workers reported the synthesis of 3-alkenylindoles from indoles and α-hydrogen-containing alkyl-/arylaldehydes by successive Brønsted acid/base catalysis (Scheme 1) [20]. The third category, which is also the most explored and popular one, involves the

[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

• reaction. In the presence of a Brønsted acid, mainly [1,3]-rearrangement is observed, whereas a Lewis acid catalyzes the [1,4]-sulfur migration. To gain insight into the mechanism of these transformations, the stereochemistry of these rearrangements have been tested, along with the conduction of some

• cationic intermediates underwent hydrolysis during aqueous workup, leading to the observed products. It was assumed that a similar sulfur atom migration should occur in the presence of Brønsted acid under dry conditions. Therefore, a set of phosphine sulfides prepared above was subjected to the reaction

• cyclopentyl and cycloheptyl fragments, which afforded the β-mercaptophosphine oxides in low yields. In order to gain insight into the reaction mechanism when using Brønsted acid, it was decided to perform the reactions at different temperatures and to monitor the reaction mixture at different times (Table 4

Microwave-assisted synthesis of 2-substituted 4,5,6,7-tetrahydro-1,3-thiazepines from 4-aminobutanol

• María C. Mollo,
• Natalia B. Kilimciler,
• Juan A. Bisceglia and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2020, 16, 32–38, doi:10.3762/bjoc.16.5

• -toxic and environmentally safe. These reagents play a dual role, as they enhance the electrophilicity of nitriles, carbonyls and carbinols, and can also react irreversibly with water. Unlike PPA, a Brønsted acid incompatible with some acid-sensitive functionalities, PPE and PPSE are aprotic and mild

Extension of the 5-alkynyluridine side chain via C–C-bond formation in modified organometallic nucleosides using the Nicholas reaction

• Renata Kaczmarek,
• Dariusz Korczyński,
• James R. Green and
• Roman Dembinski

Beilstein J. Org. Chem. 2020, 16, 1–8, doi:10.3762/bjoc.16.1

• -acetate hexacarbonyl dicobalt complexes and a Lewis or Brønsted acid. A range of heteroatom nucleophiles have been incorporated into alkyne dicobalt complexes by this chemistry [34][35][36][37][38][39][40]. However, reactions with carbon-based nucleophiles provide an opportunity to access the structurally

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• sesquiterpenes (type I TCs), diterpenes can either be generated by type I TCs or type II TCs [11][55]. Type II TCs initiate carbocation formation by Brønsted acid catalysis to protonate a terminal isoprene double bond or an epoxide ring (Figure 5b) [56]. Thus, cyclization mediated by type II TCs leads to an

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• Sodeoka and co-workers in 2012 [131]. The reaction was carried out with Togni’s reagent as the CF3 source and TsOH as a Brønsted acid in CH2Cl2 at 40 °C (Scheme 71). Notably, trifluoromethylstyrenes were formed through further transformations of the oxytrifluoromethylated products with high efficiency. In

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

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• , the trans-decalin scaffold is the ideal objective of numerous methodology studies. Inspired by nature’s highly efficient and stereochemically controlled syntheses of terpenes, up to now, various synthetic strategies to trans-decalin have been developed, e.g., Brønsted acid or Lewis acid-mediated

Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• rearrangement has been developed using a chiral Brønsted acid based on pentacarboxycyclopentadiene (PCCP). This reaction provides rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks from readily available starting material and is operationally simple. Keywords: aza-Piancatelli; Brønsted

• aza-Piancatelli reaction, we sought to identify other asymmetric catalytic systems capable of controlling the absolute stereochemistry. To this end, we envisioned that the chiral pentacarboxycyclopentadiene (PCCP) Brønsted acid catalyst (8) recently developed by the Lambert lab might be suitable

• (Figure 1) [38]. First, the pKa values measured in acetonitrile (MeCN) are lower than chiral phosphoric acids (Brønsted acid pKa = 8.85 vs chiral phosphoric acids pKa = 12–14) [38]. Given the enhanced acidity, we reasoned that this type of chiral Brønsted acid catalyst could facilitate the dehydration

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

• example, alcohol 18 provides a mixture of products 19 and 20 in a 32:68 ratio, presumably through the pentacation 5 (Scheme 5). Even with the use of the stronger Brønsted acid, CF3SO3H–SbF5, significant quantities of the cyclization product 20 are observed. This raises an obvious question: why does

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

• [22][23][24][25], Ir [26], Rh [27][28], and Co [29]. However, only electron-rich allenes, bearing electron-donating substituents, take part in the metal-catalyzed reactions. There are just a few examples of Brønsted acid catalyzed intermolecular hydroarylations of allenes by electron-rich arenes

• carried out a large-scale one-pot solvent-free synthesis of amides 6a,b starting from propargyl alcohols 7a,b at room temperature (Scheme 4). At the first step, alcohols 7a,b in the reaction with PCl3 were transformed into the corresponding allenes 1a,h. Then, the addition of Brønsted acid (TfOH or H2SO4

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

• activation of alcohols [24], epoxide opening [25][26], Friedel–Crafts alkylations [27], dehydrative glycosylation [28] and many other reactions [29][30][31]. The robustness and mildness of organoboronic acid catalysts in comparison to traditional strong Lewis and Brønsted acid catalysts inspired us to

Mechanochemical synthesis of hyper-crosslinked polymers: influences on their pore structure and adsorption behaviour for organic vapors

• Sven Grätz,
• Sebastian Zink,
• Hanna Kraffczyk,
• Marcus Rose and
• Lars Borchardt

Beilstein J. Org. Chem. 2019, 15, 1154–1161, doi:10.3762/bjoc.15.112

• –Teller) surface areas of up to 2000 m2g−1 for fully amorphous materials [10]. Typically, chloromethyl or methoxy groups are used to crosslink aromatic building blocks by using stoichiometric or even excess amounts of FeCl3 as catalyst. Recently, also a metal-free Brønsted acid-catalyzed reaction using

The LANCA three-component reaction to highly substituted β-ketoenamides – versatile intermediates for the synthesis of functionalized pyridine, pyrimidine, oxazole and quinoxaline derivatives

• Tilman Lechel,
• Roopender Kumar,
• Mrinal K. Bera,
• Reinhold Zimmer and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2019, 15, 655–678, doi:10.3762/bjoc.15.61

• , KE30, KE31 and KE35 (Table 1, entries 2, 23, 30, 31, and 35). The present approach does not allow the synthesis of β-ketoenamides with substituents R2 = H or R3 = H. The reaction of lithiated methoxyallene with hydrogen cyanide as second component was not examined due to the assumed Brønsted acid