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

Naphthalene diimide bis-guanidinio-carbonyl-pyrrole as a pH-switchable threading DNA intercalator

• Poulami Jana,
• Filip Šupljika,
• Carsten Schmuck and
• Ivo Piantanida

Beilstein J. Org. Chem. 2020, 16, 2201–2211, doi:10.3762/bjoc.16.185

• naphthalene diimde analogue (NDI) equipped at the imide positions with two guanidinio-carbonyl-pyrrole (GCP) pendant arms interacted significantly stronger with ds-DNA at pH 5 than at pH 7, due to reversible protonation of the GCP arms. This was consequence of a pH-switchable threading intercalation into ds

• -DNAs only at pH 5, while at neutral conditions (pH 7) NDI-GCP2 switched to the DNA minor groove binding. Intriguingly, NDI-GCP2 was at both pH values studied bound to the ds-RNA major groove, still showing a higher affinity and thermal denaturation effect at pH 5 due to GCP protonation. At excess over

• not observe any emission, neither for single dye binding to DNA, nor in crowding conditions (excess of dye over DNA binding sites) at which eventually fluorescent excimers could be formed. Interactions with DNA/RNA Because of significant differences in the protonation states of compound 4, studies

Regioselective cobalt(II)-catalyzed [2 + 3] cycloaddition reaction of fluoroalkylated alkynes with 2-formylphenylboronic acids: easy access to 2-fluoroalkylated indenols

• Tatsuya Kumon,
• Miroku Shimada,
• Jianyan Wu,
• Shigeyuki Yamada and
• Tsutomu Konno

Beilstein J. Org. Chem. 2020, 16, 2193–2200, doi:10.3762/bjoc.16.184

• insertion into the formyl moiety to afford the corresponding cobalt alkoxide Int-3a, (4) protonation of Int-3a with HX (X = acac, OiPr, or OH), giving rise to the desired 2-fluoroalkylated indenol 3. The formation of the 3-fluoroalkylated indanones as a side product may be explained based on the previous

• to the electron-withdrawing ability of the fluoroalkyl group. The Int-5b species undergoes protonation at the carbon bonded to the fluoroalkyl group, giving the enol Int-6b. Finally, the enol Int-6b produces the 3-fluoroalkylated indanone 5 via keto–enol tautomerism. Conclusion In conclusion, we

Regiodivergent synthesis of functionalized pyrimidines and imidazoles through phenacyl azides in deep eutectic solvents

• Paola Vitale,
• Luciana Cicco,
• Ilaria Cellamare,
• Filippo M. Perna,
• Antonio Salomone and
• Vito Capriati

Beilstein J. Org. Chem. 2020, 16, 1915–1923, doi:10.3762/bjoc.16.158

• undergo a base-promoted loss of nitrogen to form α-imino ketones upon protonation [38]. A plausible mechanism for the formation of pyrimidine derivative 7a from 2a, in competition with imidazoles 3a/3a', is depicted in Scheme 5. The key intermediate 5a, formed by elimination of nitrogen from the enol

One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway

• Esra Demir,
• Ozlem Sari,
• Yasin Çetinkaya,
• Ufuk Atmaca,
• Safiye Sağ Erdem and
• Murat Çelik

Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148

• RC1 (7f+CSI) (Figure 5). Paths 1a and 1b represent the protonation of the ring nitrogen by one and two water molecules, respectively, and the departure of 12. In path 1a, the transformation of the TS2 to 9f involves the shortening of the N4–H8 distance from 1.46 to 1.01 Å and S6–O7 distance from 1.89

Tuneable access to indole, indolone, and cinnoline derivatives from a common 1,4-diketone Michael acceptor

• Dalel El-Marrouki,
• Sabrina Touchet,
• Abderrahmen Abdelli,
• Hédi M’Rabet,
• Mohamed Lotfi Efrit and
• Philippe C. Gros

Beilstein J. Org. Chem. 2020, 16, 1722–1731, doi:10.3762/bjoc.16.144

• , leading to an intermediate enol that, after a keto–enol equilibrium and aromatization, gives the indolone 7. For the indole 6 and the cinnoline 8, the synthesis starts with the protonation of the oxygen atom of the conjugated carbonyl group of the 1,4-diketone, followed by an imine formation between the

Rearrangement of o-(pivaloylaminomethyl)benzaldehydes: an experimental and computational study

• Csilla Hargitai,
• Györgyi Koványi-Lax,
• Tamás Nagy,
• Péter Ábrányi-Balogh,
• András Dancsó,
• Gábor Tóth,
• Judit Halász,
• Angéla Pandur,
• Gyula Simig and
• Balázs Volk

Beilstein J. Org. Chem. 2020, 16, 1636–1648, doi:10.3762/bjoc.16.136

• , gave isomeric aldehyde 2a (48%) and the dimer-like racemic product 3a (11%). Both transformations were rationalized by the intermediacy of the isoindole 4a (Scheme 1). The formation of aldehyde 2a can be explained by a protonation of the ring tautomer 1a, followed by an acid-catalyzed water elimination

• explained by the protonation of ring tautomers 9 to 10 (Scheme 4), followed by a water elimination, and subsequent deprotonation of cations 11 to afford isoindoles 4 [3][4][5]. The protonation of the latter [6], followed by the attack of water at position 1 of cations 12, and subsequent deprotonation of

• turned out that the acid catalyst (TFA in this case), as expected, had a crucial role in the protonation and deprotonation as well as in the dehydration and hydration elementary steps of the reaction sequence. Without catalyst, the 9a→11a→4a transformations required an energy investment of 150.7 and