Switchable molecular tweezers: design and applications

• Pablo Msellem,
• Maksym Dekthiarenko,
• Nihal Hadj Seyd and
• Guillaume Vives

Beilstein J. Org. Chem. 2024, 20, 504–539, doi:10.3762/bjoc.20.45

• ligand (such as pyridine or pyrazine), valence tautomerism from ligand-centered oxidation to a metal-centered one is achieved due to the stabilization of an octahedral Ni(III). These properties allow the tweezers to reach six distinct and stable states by playing with three orthogonal stimuli that are

Synthesis of spiropyridazine-benzosultams by the [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes

• Wenqing Hao,
• Long Wang,
• Jinlei Zhang,
• Dawei Teng and
• Guorui Cao

Beilstein J. Org. Chem. 2024, 20, 280–286, doi:10.3762/bjoc.20.29

• benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes (Scheme 1). Results and Discussion To initiate our studies, 3-ethylbenzo[d]isothiazole 1,1-dioxide (1a) and α-halogeno hydrazone 2a were selected as the model substrates. Our aim was to explore the possibility of enamine–iminium tautomerism of N-sulfonyl

Investigation of cationic ring-opening polymerization of 2-oxazolines in the “green” solvent dihydrolevoglucosenone

• Solomiia Borova and
• Robert Luxenhofer

Beilstein J. Org. Chem. 2023, 19, 217–230, doi:10.3762/bjoc.19.21

• which interfere with the cationic ring-opening polymerization of 2-oxazolines (Figure 5). It has been reported that DLG can undergo keto–enol tautomerism and form enols or can participate in nucleophilic addition reactions [49]. Furthermore, it can react with water to its hydrated form, a geminal diol

Experimental and theoretical studies on the synthesis of 1,4,5-trisubstituted pyrrolidine-2,3-diones

• Nguyen Tran Nguyen,
• Vo Viet Dai,
• Nguyen Ngoc Tri,
• Luc Van Meervelt,
• Nguyen Tien Trung and
• Wim Dehaen

Beilstein J. Org. Chem. 2022, 18, 1140–1153, doi:10.3762/bjoc.18.118

• /bjoc.18.118 Abstract Substituted 4-acetyl-3-hydroxy-3-pyrroline-2-ones have been prepared via three-component reactions and the tautomerism of these 3-pyrroline-2-ones is due to the slight difference of energy, and the significantly large rate constant of transformation between two tautomers. 1,4,5

• NMR spectrum of 4c in CDCl3 showed sharp peaks at 29.21 ppm and 194.61 ppm representing the two carbon atoms of the acetyl group attached to the 4-postion of the heterocyclic five-membered ring. Therefore, the broadening of peaks observed in the 13C NMR spectra is due to the tautomerism of compounds

• carbon atoms of the acetyl group is due to the tautomerism of 4-acetyl-3-hydroxy-3-pyrrolin-2-ones in DMSO. The isomers 4a and 4a’ exist together upon synthesis with the significantly large rate constant of transformation of 4a into 4a’ of ca. 1012 s−1 in the gas phase and solvents mode (ethanol

A trustworthy mechanochemical route to isocyanides

• Francesco Basoccu,
• Federico Cuccu,
• Federico Casti,
• Rita Mocci,
• Claudia Fattuoni and
• Andrea Porcheddu

Beilstein J. Org. Chem. 2022, 18, 732–737, doi:10.3762/bjoc.18.73

• mechanism (Scheme 4). The single equivalent of triethylamine should be able to activate the tautomerism of the formamide through an acid–base reaction [33][42][43][44][45]. The triethylammonium salt produced can be restored as triethylamine through the action of Na2CO3. This proton transfer allows the

Asymmetric organocatalytic Michael addition of cyclopentane-1,2-dione to alkylidene oxindole

• Estelle Silm,
• Ivar Järving and
• Tõnis Kanger

Beilstein J. Org. Chem. 2022, 18, 167–173, doi:10.3762/bjoc.18.18

• versatile starting materials in organic synthesis [1][2]. Specifically, due to their keto–enol tautomerism and high reactivity, diketones are excellent precursors for different pharmaceuticals [3]. Cyclic 1,3-diketones have been widely exploited to access enantiomerically enriched scaffolds with increased

1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis

• Ruan Carlos B. Ribeiro,
• Patricia G. Ferreira,
• Amanda de A. Borges,
• Luana da S. M. Forezi,
• Fernando de Carvalho da Silva and
• Vitor F. Ferreira

Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5

• cleaner and form the substitution product at position C4. Fieser and Fieser were the first to study tautomerism between 4-arylamino-1,2-naphthoquinone A and 2-hydroxy-1,4-naphthoquinone-4-arylimine B (Scheme 3C) using the redox potential compared to the pH of the medium. It was observed that

• + was developed by Gates and Newhall in 1948 [107]. Land and co-workers demonstrated that cyanomethyl derivatives of ortho-quinones undergo facile tautomerism to para-quinomethanes [108]. Villemin and co-workers summarized these reactions, which were expanded to several other condensation products with

Stereoselective synthesis and transformation of pinane-based 2-amino-1,3-diols

• Ákos Bajtel,
• Mounir Raji,
• Matti Haukka,
• Ferenc Fülöp and
• Zsolt Szakonyi

Beilstein J. Org. Chem. 2021, 17, 983–990, doi:10.3762/bjoc.17.80

• -amino-1,3-diols, which underwent a regioselective ring closure with formaldehyde or benzaldehyde delivering pinane-condensed oxazolidines. During the preparation of 2-phenyliminooxazolidine, an interesting ring–ring tautomerism was observed in CDCl3. Keywords: 2-amino-1,2-diol; monoterpene; oxazolidin

• -2-one; stereoselective; tautomerism; Introduction The best known 2-amino-1,3-diol derivative sphingosine (1) plays a crucial role in intracellular signaling as second messenger, and its derivatives called sphingolipids are also critical for cell growth, cell differentiation, cell recognition, and

• conditions (Scheme 6). The proposed reaction pathway for the ring–ring tautomerism of 21A and 21B is presented in Figure 4 and it explains why the acidic environment (present generally in CDCl3 solution) is necessary. In a similar manner, an oxazolidine–1,3-oxazine tautomerism of pulegone-based 3-amino-1,2

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

• reaction with 2-(nitromethylene)hexahydropyrimidine B (obtained by reaction between 92 and 91) resulting in intermediate C. The nucleophilic addition of secondary amino to cyano group affords an intermediate D engaging in imine–enamine tautomerism and finally leads to desired products 94 (Scheme 35

• 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

Amino- and polyaminophthalazin-1(2H)-ones: synthesis, coordination properties, and biological activity

• Zbigniew Malinowski,
• Emilia Fornal,
• Agata Sumara,
• Renata Kontek,
• Karol Bukowski,
• Beata Pasternak,
• Dariusz Sroczyński,
• Joachim Kusz,
• Magdalena Małecka and
• Monika Nowak

Beilstein J. Org. Chem. 2021, 17, 558–568, doi:10.3762/bjoc.17.50

• reported by us [30]. It is known that the alkylation of phthalazinones depends on the reaction conditions and can proceed in two ways involving either the nitrogen or the oxygen atom (lactam–lactim tautomerism). It has been proven that potassium salts of phthalazinones or the bromo derivatives are

• (m/z = 422.3 and 424.3 Da) showed at the first step the loss of an aminoalkyl fragment (C2H3NMe2 = 71.1 Da) to form the ions 9 ⇌ 10 (m/z = 351.2 and 353.2 Da). Because of the lactam–lactim tautomerism the further complex decomposition can proceed through two fragmentation routes: 1) with the loss of

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

• 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

One-pot and metal-free synthesis of 3-arylated-4-nitrophenols via polyfunctionalized cyclohexanones from β-nitrostyrenes

• Haruyasu Asahara,
• Minami Hiraishi and
• Nagatoshi Nishiwaki

Beilstein J. Org. Chem. 2020, 16, 1830–1836, doi:10.3762/bjoc.16.150

• products were obtained. The aromatization is considered to proceed as shown in Scheme 4. After the iodization at the 4-position, which leads to the formation of the intermediate 6, the aromatization is achieved by the successive elimination of hydrogen iodide and methanol, with concurrent tautomerism to

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

• ; ring-chain tautomerism; Introduction In a preliminary publication [1] we disclosed that methylenedioxy-substituted o-(pivaloylaminomethyl)benzaldehyde (1a), when kept in dichloromethane (DCM) in the presence of a catalytic amount (0.13 equiv) of trifluoroacetic acid (TFA) for 72 h at room temperature

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• interaction due to matching or inverted energy levels between metal and ligand leads to valence tautomerism [5][6][7][8], which paves the way for orchestrated electronic events occurring within the metal complex and influences the chemical reactivity of the complex. While the field of catalysis with redox

• approaches are only emerging and should blossom in the near future. In order to assert this field as a true game-changer in copper catalysis, further work should aim at rationalizing the “redox dialogue” between the metal and the ligand, and provide a deeper understanding of the valence tautomerism at work

In water multicomponent synthesis of low-molecular-mass 4,7-dihydrotetrazolo[1,5-a]pyrimidines

• Irina G. Tkachenko,
• Sergey A. Komykhov,
• Vladimir I. Musatov,
• Svitlana V. Shishkina,
• Viktoriya V. Dyakonenko,
• Vladimir N. Shvets,
• Mikhail V. Diachkov,
• Valentyn A. Chebanov and
• Sergey M. Desenko

Beilstein J. Org. Chem. 2019, 15, 2390–2397, doi:10.3762/bjoc.15.231

• -withdrawing properties of the tetrazole ring, which makes them useful for studying various theoretical issues, e.g., tautomerism [5], intramolecular transformations [6], etc. There are several approaches to the synthesis of 4,7-dihydrotetrazolo[1,5-a]pyrimidines. Two of them make use of 5-aminotetrazole as a

Installation of -SO₂F groups onto primary amides

• Jing Liu,
• Shi-Meng Wang,
• Njud S. Alharbi and
• Hua-Li Qin

Beilstein J. Org. Chem. 2019, 15, 1907–1912, doi:10.3762/bjoc.15.186

• tautomerism of amides [43] may occur in the reaction process and the tautomer 3e could react with Na2SO4 to generate 4e, which indicated that N–H connected with two electron-withdrawing groups (carbonyl, and SO2F) can behave as an acid to donate a proton for chemical transformations. This property of

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

• Vera Deneva,
• Georgi Dobrikov,
• Aurelien Crochet,
• Daniela Nedeltcheva,
• Katharina M. Fromm and
• Liudmil Antonov

Beilstein J. Org. Chem. 2019, 15, 1898–1906, doi:10.3762/bjoc.15.185

• , Switzerland 10.3762/bjoc.15.185 Abstract The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has

• solvents. Strong bathochromic and hyperchromic effects in the visible spectra accompany the 1:1 formation of complexes with some alkaline earth metal ions. Keywords: amide group; azo dye; molecular sensor; sidearm; tautomerism; Introduction The design of new organic sensing systems is an undividable part

• tautomeric proton exchange has the same properties when the equilibrium is switched from one to the other tautomer. The tautomerism can be controlled by metal ion addition, when an ionophore unit is implemented in the tautomeric backbone. The conceptual idea to achieve the pure enol tautomer through

Synthesis of non-racemic 4-nitro-2-sulfonylbutan-1-ones via Ni(II)-catalyzed asymmetric Michael reaction of β-ketosulfones

• Alexander N. Reznikov,
• Anastasiya E. Sibiryakova,
• Marat R. Baimuratov,
• Eugene V. Golovin,
• Victor B. Rybakov and
• Yuri N. Klimochkin

Beilstein J. Org. Chem. 2019, 15, 1289–1297, doi:10.3762/bjoc.15.127

• more rapid than the epimerization of product 8a. After about 60 hours the content of sulfone 5a in solution became almost constant, while the amount of epimer 9a continued to increase. This fact may indicate that the formation of compound 9a may occur not only as a result of keto–enol tautomerism in

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines

• Andrejs Šišuļins,
• Jonas Bucevičius,
• Yu-Ting Tseng,
• Irina Novosjolova,
• Kaspars Traskovskis,
• Ērika Bizdēna,
• Huan-Tsung Chang,
• Sigitas Tumkevičius and
• Māris Turks

Beilstein J. Org. Chem. 2019, 15, 474–489, doi:10.3762/bjoc.15.41

• –3.95 (m, γ) and the broadening of signals at 7.69 (s, a), 4.04 (t, b) and 3.84–3.74 (m, c). A similar type of the ring–chain tautomerism is expected to occur in 6-azido-2-amino-7-deazapurines (synthetic intermediates on the way 3→10/11), but it was not studied in detail due to their relatively low

• stability [39]. Regarding the tautomerism in 2,6-diazido-substituted starting materials, it has been studied previously for both purine [41] and 7-deazapurine [52] derivatives. In both cases practically only the diazido forms are observed in chloroform solution, but the proportion of the tetrazole tautomer

Synthesis of functionalised β-keto amides by aminoacylation/domino fragmentation of β-enamino amides

• Pavel Yanev and
• Plamen Angelov

Beilstein J. Org. Chem. 2018, 14, 2602–2606, doi:10.3762/bjoc.14.238

• resolved NMR spectra. Similar tautomerism was observed in 11d,b,g,k (n = 3), but with negligible proportion of the ring tautomer. Conclusion In conclusion, we have demonstrated that N-protected γ-amino-β-keto amides and ω-amino-β-keto amides can be obtained from amino acids and β-enamino amides through the

• –chain tautomerism in compounds 11b,c,f,j (n = 2) and reduction to the corresponding β-hydroxy amides 12. Yields of compounds 3 and 5 (R1 = Ph, n = 0), obtained according to Scheme 1 and Scheme 2. Yields of compounds 4 and 11 (R2 = R3 = H), obtained according to Scheme 1 and Scheme 6. Supporting

Microwave-assisted synthesis of biologically relevant steroidal 17-exo-pyrazol-5'-ones from a norpregnene precursor by a side-chain elongation/heterocyclization sequence

• Gergő Mótyán,
• László Mérai,
• Márton Attila Kiss,
• Zsuzsanna Schelz,
• Izabella Sinka,
• István Zupkó and
• Éva Frank

Beilstein J. Org. Chem. 2018, 14, 2589–2596, doi:10.3762/bjoc.14.236

• , keto–enol tautomerism can be challenging and is of special importance in biological systems, chemical reactivity, and molecular recognition [18]. The tautomeric equilibrium in solution is strongly influenced by the substitution pattern of the heterocyclic ring, the polarity and protic nature of the

• , a subsequent derivatization with acetic anhydride in pyridine to afford 8, allowed its structure verification indirectly. This derivatization did not only improve the solubility of the compound, but also eliminated the possibility of prototropic tautomerism through acetylation of both the amino and

Determining the predominant tautomeric structure of iodine-based group-transfer reagents by ¹⁷O NMR spectroscopy

• Nico Santschi,
• Cody Ross Pitts,
• Benson J. Jelier and
• René Verel

Beilstein J. Org. Chem. 2018, 14, 2289–2294, doi:10.3762/bjoc.14.203

• for the design of electrophilic transfer reagents. A particularly intriguing aspect is the fundamental II–IIII tautomerism about the hypervalent bond, which has led in certain cases to a surprising re-evaluation of the classic hypervalent structure. Thus, through a combination of 17O NMR spectroscopy

• can be used to gain insight into the solution-phase tautomerism observed in iodine-based group-transfer reagents. In particular, we confirm that Shen’s revised, electrophilic SCF3-transfer reagent adopts an "acyclic" thioperoxide tautomeric form in solution whereas an electrophilic cyanide source

• structural analysis. Tautomerism in iodine-based group-transfer reagents probed by 17O NMR spectroscopy (A) and key structures investigated herein (B). Assignment of acyclic (b) and cyclic (a) structures to 5 and 6, respectively, based on computed isotropic shift values (δiso) and experimental 17O NMR

¹⁵N-Labelling and structure determination of adamantylated azolo-azines in solution

• Sergey L. Deev,
• Alexander S. Paramonov,
• Tatyana S. Shestakova,
• Igor A. Khalymbadzha,
• Oleg N. Chupakhin,
• Julia O. Subbotina,
• Oleg S. Eltsov,
• Pavel A. Slepukhin,
• Vladimir L. Rusinov,
• Alexander S. Arseniev and
• Zakhar O. Shenkarev

Beilstein J. Org. Chem. 2017, 13, 2535–2548, doi:10.3762/bjoc.13.250

• this approach for the syntheses of 15N-labelled tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines [25] starting from 15N-labelled 5-aminotetrazole. However, due to proton tautomerism, the use of single-labelled [2-15N]-5-aminotetrazole led to the formation of isotopomer mixtures, which

Asymmetric synthesis of propargylamines as amino acid surrogates in peptidomimetics

• Matthias Wünsch,
• David Schröder,
• Tanja Fröhr,
• Lisa Teichmann,
• Sebastian Hedwig,
• Nils Janson,
• Clara Belu,
• Jasmin Simon,
• Shari Heidemeyer,
• Philipp Holtkamp,
• Jens Rudlof,
• Lennard Klemme,
• Alessa Hinzmann,
• Beate Neumann,
• Hans-Georg Stammler and
• Norbert Sewald

Beilstein J. Org. Chem. 2017, 13, 2428–2441, doi:10.3762/bjoc.13.240

• structure analysis. Due to the extended π-system of the α,β-unsaturated imines 12i and 12k, the progress of the propargylamide–allenylamide rearrangement that eventually leads to the formation of the α,β-unsaturated imines by tautomerism could be easily monitored by UV–vis spectroscopy. The reaction mixture

• turned brightly yellow when treated with bases like piperidine. The X-ray crystal structures of 11i and 12i confirm unequivocally the structure of the products and thus the postulated two-step rearrangement. Both, the rearrangement of the alkyne to the allene and the subsequent tautomerism to the α,β

Synthesis of tetrasubstituted pyrazoles containing pyridinyl substituents

• Josef Jansa,
• Ramona Schmidt,
• Ashenafi Damtew Mamuye,
• Laura Castoldi,
• Alexander Roller,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2017, 13, 895–902, doi:10.3762/bjoc.13.90

• tautomerism of compound 1a. Supporting Information Supporting Information File 344: Experimental details and characterization data. Acknowledgements We thank Mrs. Fatehme Keramati for experimental contributions. Josef Jansa thanks Palacký University for awarding a study visit at the University of Vienna