Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

• Shivani Gulati,
• Stephy Elza John and
• Nagula Shankaraiah

Beilstein J. Org. Chem. 2021, 17, 819–865, doi:10.3762/bjoc.17.71

• -proliferative activity against tumor cell lines leading to the discovery of new lead compounds (Scheme 6). A tentative mechanism in Scheme 7 depicts the formation of iminium ion A from the reaction between 19 and 20 after the intramolecular protonation by carboxylic acid. The A conformer stabilized by

• the allene intermediate D. Finally, an intramolecular 6π-electrocyclization and tautomerism results in the desired products 143a. The authors proposed a mechanism for azepinoindoles (Scheme 59) [128] wherein acid-catalyzed protonation of arylglyoxal monohydrate followed by dehydration and addition of

Synthesis of β-triazolylenones via metal-free desulfonylative alkylation of N-tosyl-1,2,3-triazoles

• Soumyaranjan Pati,
• Renata G. Almeida,
• Eufrânio N. da Silva Júnior and
• Irishi N. N. Namboothiri

Beilstein J. Org. Chem. 2021, 17, 762–770, doi:10.3762/bjoc.17.66

• , triazoles 1b and 1c containing electron donating 4-tolyl and 4-methoxyphenyl groups did not deliver the products 3b and 3c, respectively, even after prolonged reaction time. This is attributable to the greater reactivity of their corresponding triazolyl anion which preferred protonation over Michael

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• equilibrium (Table 4, entries 7 and 11 vs entries 1 and 9). Attempts to influence the diastereomeric ratio of the cyclization products by irreversible stoichiometric deprotonation of the lactams 12d,f,i by LDA at −78 °C and subsequent protonation by methanol did not lead to substantial changes of the initial

Mesoionic tetrazolium-5-aminides: Synthesis, molecular and crystal structures, UV–vis spectra, and DFT calculations

• Vladislav A. Budevich,
• Sergei V. Voitekhovich,
• Alexander V. Zuraev,
• Vadim E. Matulis,
• Vitaly E. Matulis,
• Alexander S. Lyakhov,
• Ludmila S. Ivashkevich and
• Oleg A. Ivashkevich

Beilstein J. Org. Chem. 2021, 17, 385–395, doi:10.3762/bjoc.17.34

• the data for 1,3-di-alkyltetrazolium-5-aminide salts as described in the literature [25][26][28][32][33][34][35]. First of all, it should be mentioned that the formation of the salt from the corresponding mesoionic compound followed by protonation of the endocyclic N atom in all cases presented in

• ), showing that the largest negative charge and the deepest minimum of MESP of 8a are located near the exocyclic atom N5, and hence it is the most preferable protonation site in 8a. The TD-tHCTHhyb/6-311+G(2d,p) calculated UV–vis spectra of compound 8a in n-hexane, THF, chloroform, methanol, and water are

• of a hydrogen bond between the exocyclic N5 atom and the solvent is taken into account (model structure in Figure 4b). For the methanol and water solutions, the agreement between the calculated and experimental spectra is observed only when the protonation of the N5 atom is taken into account (model

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

• , and triflate 45f, which was isolated after basic workup of the reaction (59% yield) [63]. Hence, protonation of 44 led to dialkoxysulfonium triflate 47 along with the release of alcohol 9g. The subsequent formation of the excellent sultine leaving group 46 (assumed to be as good of a leaving group as

• , Pittman, et al. investigated the protonation of a variety of trifluoromethyl ketones in a superacid [35][91]. Trifluoromethyl ketone protonation was observed by NMR spectroscopy at −60 °C in a superacidic FSO3H–SbF5–SO2 solution (Scheme 34). The 19F chemical shift variation for the generated oxygen

• ] (Scheme 38). In these reactions, oxygen-stabilized α-(trifluoromethyl)carbenium ions 142 are supposed to be generated by protonation or Lewis acid activation of the starting ketones. Klumpp et al. explored the reactivity of CF3-substituted superelectrophiles (defined as multiply charged cationic

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

• traces of the 1,4-dihydropyridazine 4af were detected following the two-step, one-pot protocol (Scheme 3). Apparently, the basic pyridine nitrogen atoms of intermediate 3af deactivate the acid catalyst, whilst the use of 3.4 equiv of TFA causes the full protonation of the pyridine rings thus making them

• (Scheme 4). A proposed mechanism for the recyclization of hydroxypyrrolines 1 with hydrazides 2 is shown in Scheme 5. The protonation of the starting hydroxypyrroline 1 with TFA leads to the formation of cation A, which reacts with hydrazide 2 to give the pyrrolidine derivative B. The latter undergoes a

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

• -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

Multiswitchable photoacid–hydroxyflavylium–polyelectrolyte nano-assemblies

• Alexander Zika and
• Franziska Gröhn

Beilstein J. Org. Chem. 2021, 17, 166–185, doi:10.3762/bjoc.17.17

•  4. Cycle I starts with the excitation of the photoacid by irradiation at λ = 300 nm with the aim to achieve the protonation of the hydroxyflavylium molecule, and the subsequent opening to the Cc form. After keeping the assemblies in the dark and addition of HCl, assemblies as in state C should

Novel library synthesis of 3,4-disubstituted pyridin-2(1H)-ones via cleavage of pyridine-2-oxy-7-azabenzotriazole ethers under ionic hydrogenation conditions at room temperature

• Romain Pierre,
• Anne Brethon,
• Sylvain A. Jacques,
• Aurélie Blond,
• Sandrine Chambon,
• Sandrine Talano,
• Catherine Raffin,
• Branislav Musicki,
• Claire Bouix-Peter,
• Loic Tomas,
• Gilles Ouvry,
• Rémy Morgentin,
• Laurent F. Hennequin and
• Craig S. Harris

Beilstein J. Org. Chem. 2021, 17, 156–165, doi:10.3762/bjoc.17.16

• ). No product was observed via direct SNAr using KOH (Table 1, entry 1) [3]. Acidic conditions (Table 1, entries 2–5) [4], where we can expect protonation thus activation of the pyridine ring towards nucleophilic attack, resulted in only traces of product along with hydrolysis of the amide moiety at C-3

• protonation and activation of the pyridine towards SNAr with HOAt (Table 4). Exploration of the C-4 amine vector As we moved forwards in the program, we were eager to develop our understanding of SARs (structure–activity relationships) from the C-4 vector. Although we could have adopted the same methodology

• the C-2–OAt ether presumably due to the lower basicity of 26 compared to 8, therefore, activation via protonation of the pyridine was not occurring. With a view to capitalize on our knowledge acquired so far on this scaffold, we decided to force the transformation to the OBt ether by SNAr under basic

Direct synthesis of anomeric tetrazolyl iminosugars from sugar-derived lactams

• Michał M. Więcław and
• Bartłomiej Furman

Beilstein J. Org. Chem. 2021, 17, 115–123, doi:10.3762/bjoc.17.12

• proton donor in the reaction mixture. Intriguingly, this behavior is inconsistent with the generally accepted mechanism of this transformation, which assumes the hydrolysis of TMSN3 to HN3 and activation of the imine species by protonation. Scheme 7 presents our proposal for the possible course of the

Synthesis of aryl 2-bromo-2-chloro-1,1-difluoroethyl ethers through the base-mediated reaction between phenols and halothane

• Yukiko Karuo,
• Ayaka Kametani,
• Atsushi Tarui,
• Kazuyuki Sato,
• Kentaro Kawai and
• Masaaki Omote

Beilstein J. Org. Chem. 2021, 17, 89–96, doi:10.3762/bjoc.17.9

• carbon atom is a reasonable process to forward the reaction with the generation of carbanion 6. Finally, the protonation of 6 by 1 or other acidic compounds, such as water molecules present in the reaction medium, would provide 2. Conclusion We exploited the reaction of various phenols with halothane to

Control over size, shape, and photonics of self-assembled organic nanocrystals

• Chen Shahar,
• Yaron Tidhar,
• Yunmin Jung,
• Haim Weissman,
• Sidney R. Cohen,
• Ronit Bitton,
• Iddo Pinkas,
• Gilad Haran and
• Boris Rybtchinski

Beilstein J. Org. Chem. 2021, 17, 42–51, doi:10.3762/bjoc.17.5

• assembly pathway rather than the equilibration at a given solvent composition. Apparently, hydrophobic interactions dominate the self-assembly, mitigating the repulsion of the charged carboxylate groups (partial protonation of the carboxylate moieties can also not be ruled out as a result of the

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

• reactivity of compounds 9. Its protonation makes the formation of a key cyclization intermediate 11 difficult. It is known that the [n]helicenes with at least one five-membered heteroaromatic ring need n ≥ 6 to become intrinsically chiral [9][10]. High-performance liquid chromatography on chiral stationary

Synthesis of tetrafluorinated piperidines from nitrones via a visible-light-promoted annelation reaction

• Vyacheslav I. Supranovich,
• Igor A. Dmitriev and
• Alexander D. Dilman

Beilstein J. Org. Chem. 2020, 16, 3104–3108, doi:10.3762/bjoc.16.260

• substitution could be catalyzed by iodide anions accumulating in the reaction mixture. Finally, the deoxygenation of the N-oxide fragment may proceed via consecutive protonation and electron-transfer steps [28]. Conclusion In summary, a one-step method for the synthesis of tetrafluorinated piperidines starting

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

• suggested that the presence of water can catalyze this reaction (proton-transport catalysis strategy) through a two-step deprotonation/protonation process [11][21][41][42][44], but in our study, preliminary calculations in the presence of water did not improve the results in Figure 5. Therefore, we focused

• protonation/deprotonation sequence. Finally, although we did not study in detail the acetate hydrolysis from XV to 15, we could confirm the higher stability (by more than 6 kcal⋅mol−1) of 15 relative to the enone isomer arising from XII, in agreement again with the experimental results. Experimental

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

• Dmitrii A. Aksenov,
• Nikolai A. Arutiunov,
• Vladimir V. Maliuga,
• Alexander V. Aksenov and
• Michael Rubin

Beilstein J. Org. Chem. 2020, 16, 2903–2910, doi:10.3762/bjoc.16.239

• , entries 2 and 3). To the contrary, an attempt to carry out the reaction in 80% PPA provided a conversion of only 6% even at 140 °C (Table 1, entry 4), whereas no reaction was observed in 100% orthophosphoric acid (Table 1, entry 5). Evidently, under acidic conditions, protonation of the primary amino

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• rearrangement after the protonation of 1 and 2 furnished exclusively the two complexes [(1•H+)(3)] and [(2•H+)(4)] (Figure 3). The reduced affinity of the cucurbit[7]uril toward the protonated diethylamino-substituted guest in combination with the concomitant increased binding for the dimethylammonium

• triggered the back cascade translocation. Excitingly, when the self-sorted system in SelfSORT-I was treated with 2-cyano-2-phenylpropanoic acid (50) [62][63] as a chemical fuel, the protonation of 49 entailed the same cascade translocation resulting in SelfSORT-II but now with the effect that it slowly

Particle size effect in the mechanically assisted synthesis of β-cyclodextrin mesitylene sulfonate

• Stéphane Menuel,
• Sébastien Saitzek,
• Eric Monflier and
• Frédéric Hapiot

Beilstein J. Org. Chem. 2020, 16, 2598–2606, doi:10.3762/bjoc.16.211

• . While the deprotonation/protonation equilibrium preferentially takes place at the 2- and 6-positions of the β-CD [29], the alkoxide located on the primary face at the 6-position is more inclined to react with the bulky mesitylenesulfonate group than the alkoxide on the secondary face at the 2-position

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

• Jannis Ludwig,
• Tobias Moje,
• Fynn Röhricht and
• Rainer Herges

Beilstein J. Org. Chem. 2020, 16, 2589–2597, doi:10.3762/bjoc.16.210

• molar extinctions of both species were determined by adding a strong axial ligand such as piperidine (to achieve almost complete coordination) and acid (TFA) (protonation of the pyridine unit to prevent coordination, completely diamagnetic). At concentrations of ≈10 µM, intermolecular coordination is

Thermodynamic and electrochemical study of tailor-made crown ethers for redox-switchable (pseudo)rotaxanes

• Henrik Hupatz,
• Marius Gaedke,
• Hendrik V. Schröder,
• Julia Beerhues,
• Arto Valkonen,
• Fabian Klautzsch,
• Sebastian Müller,
• Felix Witte,
• Kari Rissanen,
• Biprajit Sarkar and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2020, 16, 2576–2588, doi:10.3762/bjoc.16.209

• ). These results suggest that both ammonium axles form a similar type of equilibrium with NDIC7, where the protonation of the tertiary amine and the complexation in a nonthreaded complex might contribute. When using BArF24− as the counterion for A1, the binding energies increase by 6–8 kJ/mol, which

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

• residues on the protein surface, are also sensitive to pH and in some cases ionic strength and type of counter ions. It is important to keep in mind that these factors can also affect the binding affinity of a ligand. The pH affects the protonation state, and thus charge, of both the protein and charged

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

• quenching cycle, generating [Ir]•−, which reduces the phthalimide ester 117 to give α-amino radicals 117• after decarboxylation. The CPA then activates the azaarene 118 through protonation and brings the two reactive species together in a hydrogen bonded complex 119, which facilitates radical addition

• al. [94] it is suggested that this reaction uses 1O2 for the oxidation, and proceeds through transition state 219‡ for the hydrogen-bonded catalysed nucleophilic addition step. Jiang et al. recently applied a similar dual catalytic system to the dehalogenative protonation of α,α-chlorofluoro ketones

• protonation furnished the desired enantioenriched α-fluoroketones 225 in excellent yields and enantioselectivities (33 examples, up to >99:1 er). Jiang et al. used a related system for the enantioselective reduction of 1,2-diketones 227 (Scheme 35a) [96]. In this case the catalyst 228 is proposed to form

Design and synthesis of a bis-macrocyclic host and guests as building blocks for small molecular knots

• Elizabeth A. Margolis,
• Rebecca J. Keyes,
• Stephen D. Lockey IV and
• Edward E. Fenlon

Beilstein J. Org. Chem. 2020, 16, 2314–2321, doi:10.3762/bjoc.16.192

• 19 provided diazide 20, albeit in low yield (14%). Protonation of 20 with HCl followed by anion exchange yielded 72% of the hexafluorophosphate salt of guest 2. The 1H NMR spectrum supports the ammonium ions of 2 as all peaks shifted downfield relative to the chemical shifts in neutral diamine 20. As

Styryl-based new organic chromophores bearing free amino and azomethine groups: synthesis, photophysical, NLO, and thermal properties

• Anka Utama Putra,
• Deniz Çakmaz,
• Nurgül Seferoğlu,
• Alberto Barsella and
• Zeynel Seferoğlu

Beilstein J. Org. Chem. 2020, 16, 2282–2296, doi:10.3762/bjoc.16.189

• . The pH-sensitive properties of all prepared Schiff bases were examined against TBAOH in DMSO, via deprotonation of the OH group in the salicylidene moiety and their reverse protonation was also investigated using TFA. The Schiff bases exhibited a bathochromic shift upon the addition of TBAOH to their

• media directly determines the pH level that affects organisms living in the corresponding area [18][19][20][21][22]. Therefore, pH-sensitive dyes play a critical role in various sensor applications for easy determination of such ions. These dyes show different spectral properties upon protonation

• donor than the phenol group [52][53]. Furthermore, trifluoroacetic acid (TFA) was added to a solution containing the deprotonated forms of dyes 8–12 in DMSO, so as to investigate the reversible protonation of the dyes. As can be seen in Figure 5, the addition of 5 equiv of TFA to a basic solution of 12

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