An unusual thionyl chloride-promoted C−C bond formation to obtain 4,4'-bipyrazolones

• Gernot A. Eller,
• Gytė Vilkauskaitė,
• Algirdas Šačkus,
• Vytas Martynaitis,
• Ashenafi Damtew Mamuye,
• Vittorio Pace and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2018, 14, 1287–1292, doi:10.3762/bjoc.14.110

• of 5-hydroxypyrazole-4-carboxylates in refluxing thionyl chloride. The obtained diesters can be transformed into the corresponding 4,4'-bipyrazoles via alkaline hydrolysis and subsequent decarboxylation. Detailed NMR spectroscopic investigations (1H, 13C, 15N) were undertaken with all products

• prepared. Moreover, the structure of a representative 5,5'-dioxo-4,4'-bipyrazole-4,4'-dicarboxylate was confirmed by X-ray crystal structure analysis. Keywords: dimerization; NMR (1H; 13C; 15N); pyrazolones; thionyl chloride; X-ray structure analysis; Introduction Many biologically active substances

• of all compounds treated within this study are indicated. Full and unambiguous assignment of 1H, 13C and nearly all 15N NMR resonances was achieved by combining standard NMR techniques [33], such as fully 1H-coupled 13C NMR spectra, APT, gs-HSQC, gs-HMBC, gs-HSQC-TOCSY, COSY, TOCSY and NOESY

Phosphodiester models for cleavage of nucleic acids

• Satu Mikkola,
• Tuomas Lönnberg and
• Harri Lönnberg

Beilstein J. Org. Chem. 2018, 14, 803–837, doi:10.3762/bjoc.14.68

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• products in small amounts namely 3(5)-methyl-5(3)-phenyl-1H-pyrazole (121) obtained by CN bond cleavage and benzoic acid (122) was also observed (Scheme 33). The structure of the regioisomer was established unequivocally by performing 1H,13C-HMQC, 1H,13C- and 1H,15N-HMBC experiments. Aqueous mediated

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

• -1H and 1H-13C NMR correlation experiments (COSY and HMBC, respectively) or nuclear Overhauser effect spectroscopy (NOESY or ROESY). The selective incorporation of 15N-labelled atoms in different positions of the heterocyclic core allowed for the use of 1H-15N (JHN) and 13C-15N (JCN) coupling

• of azolo-azines and 1-adamatanol in TFA solution. For azolo-1,2,4-triazinones, the formation of mixtures of N-adamantyl derivatives was observed. The JHN and JCN values were measured using amplitude-modulated 1D 1H spin-echo experiments with the selective inversion of the 15N nuclei and line-shape

• analysis in the 1D 13С spectra acquired with selective 15N decoupling, respectively. Additional spin–spin interactions were detected in the 15N-HMBC spectra. NMR data and DFT (density functional theory) calculations permitted to suggest a possible mechanism of isomerization for the adamantylated products

Synthesis, effect of substituents on the regiochemistry and equilibrium studies of tetrazolo[1,5-a]pyrimidine/2-azidopyrimidines

• Elisandra Scapin,
• Paulo R. S. Salbego,
• Caroline R. Bender,
• Alexandre R. Meyer,
• Anderson B. Pagliari,
• Tainára Orlando,
• Geórgia C. Zimmer,
• Clarissa P. Frizzo,
• Helio G. Bonacorso,
• Nilo Zanatta and
• Marcos A. P. Martins

Beilstein J. Org. Chem. 2017, 13, 2396–2407, doi:10.3762/bjoc.13.237

• the azide in both solvents evaluated. Unexpectedly, the tetrazole form is slightly more stable in CDCl3 when CX3 is bonded at the 7-position of the ring. Moreover, the 15N NMR analysis was carried out for compounds 6a and 6g. The spectra of the phenyl-substituted compound 6a, in CDCl3, showed a signal

• at δ 114.8, which is consistent with sp3 nitrogen. This signal was attributed to N1. The N5, N4, N2, and N3 atoms appear at δ 237.1, 241.3, 252.4, and 265.7, respectively. The data obtained from the 15N NMR spectrum confirms the structure of trifluoromethylated tetrazolo[1,5-a]pyrimidines in solution

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

• catalysts turned out to be the method of choice to obtain the desired tetrasubstituted pyrazoles. The formation of different unexpected reaction products is described. Detailed NMR spectroscopic investigations (1H, 13C, 15N) were undertaken with all products prepared. Moreover, the structure of a

• condensation product was confirmed by crystal structure analysis. Keywords: Negishi coupling; NMR (1H; 13C; 15N); pyrazole; pyridine; X-ray structure analysis; Introduction The pyrazole nucleus is a frequently occurring motif in many pharmaceuticals [1][2] and biologically active compounds [3][4

• spectra. The marked decrease of the 15N chemical shift of the nitrogen atom of the pyridine attached at pyrazole C-5 compared to those of the corresponding nitrogen atoms in compounds 2a,b and 3a,b (whereas the 15N shift of the pyridine moiety attached to pyrazole C-3 only slightly differs for compounds

Metal-free hydroarylation of the side chain carbon–carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

• Anna S. Zalivatskaya,
• Dmitry S. Ryabukhin,
• Marina V. Tarasenko,
• Alexander Yu. Ivanov,
• Irina A. Boyarskaya,
• Elena V. Grinenko,
• Ludmila V. Osetrova,
• Eugeniy R. Kofanov and
• Aleksander V. Vasilyev

Beilstein J. Org. Chem. 2017, 13, 883–894, doi:10.3762/bjoc.13.89

• protonation at N2, there should not be any correlation between the proton attached to N2 and Hα. The assignment of all signals in the 1H and 13C NMR spectra of cations Ca and Cm was undertaken on the basis of 1H–13C HSQC and 1H–15N HSQC spectra (see spectra in Supporting Information File 1). According to the

• groups. Selected 1H, 13C, 15N NMR data for cations Ca and Cm generated by protonation of oxadiazoles 1a and 1m at the N4 nitrogen (FSO3H, −80 °C for Ca, and −60 °C for Cm, with CH2Cl2 as internal standard). X-ray crystal structures of compounds 2a (left) (CCDC 1526767) and 2m (right) (CCDC 1526105

Isoxazole derivatives as new nitric oxide elicitors in plants

• Anca Oancea,
• Emilian Georgescu,
• Florentina Georgescu,
• Alina Nicolescu,
• Elena Iulia Oprita,
• Catalina Tudora,
• Lucian Vladulescu,
• Marius-Constantin Vladulescu,
• Florin Oancea and
• Calin Deleanu

Beilstein J. Org. Chem. 2017, 13, 659–664, doi:10.3762/bjoc.13.65

• unambiguously assigned on the basis of chemical and spectral analysis (IR, 1H, 13C and 15N NMR spectra). NMR spectra clearly indicated the presence of only one regioisomer for all synthesized 3,5-disubstituted isoxazoles. Signals in 1H and 13C NMR spectra were fully assigned based on H,C-HSQC and H,C-HMBC

• Supporting Information File 200: Experimental procedures, characterization data, IR, 1H, 13C and 15N NMR data for all new compounds and fluorescence microscopy images of NO and ROS generation for all 3,5-disubstituted isoxazoles-treated Arabidopsis leaves. Acknowledgments This work was supported by the

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• (15i–k). A series of aliphatic α-iminonitriles also gave good results (15n,o). Notably the labile dimethylacetal group tolerates this two-step transformation (15m). Using this protocol, the authors described a total synthesis of (±)-isoretronecanol (19), a pyrrolizidine alkaloid (Scheme 9). In this

Dynamics and interactions of ibuprofen in cyclodextrin nanosponges by solid-state NMR spectroscopy

• Monica Ferro,
• Franca Castiglione,
• Nadia Pastori,
• Carlo Punta,
• Lucio Melone,
• Walter Panzeri,
• Barbara Rossi,
• Francesco Trotta and
• Andrea Mele

Beilstein J. Org. Chem. 2017, 13, 182–194, doi:10.3762/bjoc.13.21

• SSNMR technique originally developed for enhancing the signal intensities of low-abundance spins, generally referred to as S spins (typically 13C, 15N, 29Si etc.) by polarization transfer from high-abundance spins, in turn labelled as I spins (usually protons). The transfer of magnetization occurs via

• resolution of the solid-state NMR signals strongly depends on the sample spinning speed, for diluted nuclei (13C or 15N) slow or moderate speeds are enough to obtain resolved spectra, while fast or very fast spinning (spinning regime >50 kHz) conditions are needed to obtain “liquid like spectra”. We begin

Characterization of the synthetic cannabinoid MDMB-CHMCZCA

• Carina Weber,
• Stefan Pusch,
• Dieter Schollmeyer,
• Sascha Münster-Müller,
• Michael Pütz and
• Till Opatz

Beilstein J. Org. Chem. 2016, 12, 2808–2815, doi:10.3762/bjoc.12.279

• -4b), 122.7 (C-4a), 120.8 (C-5), 120.1 (C-4), 119.7 (C-6), 109.6 (C-8), 109.9 (C-1), 60.4 (C-1'), 52.1 (OCH3), 49.9 (C-1''), 38.3 (C-2''), 35.4 (C-2'), 31.6 (C-3'', C-7''), 26.9 (C(CH3)3), 26.4 (C-5''), 25.9 (C-4'', C-6''); [1H,15N]-HSQC, [1H,15N]-HMBC (600 MHz, CDCl3) δN/ppm 120.9 (N-9), 106.3 (CONH

• 13C chemical shifts (δ) were referenced to the residual solvent signal as internal standard (δH = 7.26 ppm and δC = 77.16 ppm) [17][18]. The 15N chemical shifts were referenced to an external standard (nitromethane in DMSO-d6, δN = 380.2 ppm) and the coupling constants (J) are reported in Hz. Melting

Thiazol-4-one derivatives from the reaction of monosubstituted thioureas with maleimides: structures and factors determining the selectivity and tautomeric equilibrium in solution

• Alena S. Pankova,
• Pavel R. Golubev,
• Alexander F. Khlebnikov,
• Alexander Yu. Ivanov and
• Mikhail A. Kuznetsov

Beilstein J. Org. Chem. 2016, 12, 2563–2569, doi:10.3762/bjoc.12.251

• interconverting E/Z-isomers at the exocyclic C=N bond (given in parentheses on Scheme 2) could be involved. Therefore we have thoroughly analyzed the spectroscopic data of thiazolidine 3a from 2D NMR experiments (NOESY, 13C,1H and 15N,1H-HSQC and HMBC) and made a full assignment of all signals. A large difference

• two forms differ by 12 ppm. The corresponding 15N–1H correlation spectra allowed determining the signal of the exocyclic amide nitrogen atom (δ ≈ 133 ppm); only one of the two thiourea nitrogen atoms could be detected in the product. A direct correlation was found between the signals of the nitrogen

• partial or full localization of this proton on the nearest oxygen atom. The NMR spectroscopic correlations described above were found for compound 3b as well. According to the 15N,1H-HMBC spectrum, the signal of the exocyclic NH proton of the A form (δH 11.00 ppm, δN ≈ 128 ppm) correlates with the

Biomimetic synthesis and HPLC–ECD analysis of the isomers of dracocephins A and B

• Viktor Ilkei,
• András Spaits,
• Anita Prechl,
• Áron Szigetvári,
• Zoltán Béni,
• Miklós Dékány,
• Csaba Szántay Jr,
• Judit Müller,
• Árpád Könczöl,
• Ádám Szappanos,
• Attila Mándi,
• Sándor Antus,
• Ana Martins,
• Attila Hunyadi,
• György Tibor Balogh,
• György Kalaus (†),
• Hedvig Bölcskei,
• László Hazai and
• Tibor Kurtán

Beilstein J. Org. Chem. 2016, 12, 2523–2534, doi:10.3762/bjoc.12.247

• uncorrected. IR spectra were recorded on a Bruker FTIR instrument. NMR measurements (1H, 13C, gCOSY, 1D NOESY and 2D NOESY, gHSQCAD, gHMBCAD) were performed on Varian 400 MHz (equipped with 5 mm OneNMR 15N-31P/{1H-19F} PFG Probe), Varian 500 MHz (equipped with 1H{13C/15N} 5 mm PFG Triple Resonance 13C

• Enhanced Cold Probe) and Varian 800 MHz (equipped with 1H{13C/15N} Triple Resonance 13C Enhanced Salt Tolerant Cold Probe) spectrometers. 1H chemical shifts are given on the delta scale as parts per million (ppm) with tetramethylsilane (TMS) as the internal standard (0.00 ppm). 13C chemical shifts are

An effective one-pot access to polynuclear dispiroheterocyclic structures comprising pyrrolidinyloxindole and imidazothiazolotriazine moieties via a 1,3-dipolar cycloaddition strategy

• Alexei N. Izmest’ev,
• Galina A. Gazieva,
• Natalya V. Sigay,
• Sergei A. Serkov,
• Valentina A. Karnoukhova,
• Vadim V. Kachala,
• Alexander S. Shashkov,
• Igor E. Zanin,
• Angelina N. Kravchenko and
• Nina N. Makhova

Beilstein J. Org. Chem. 2016, 12, 2240–2249, doi:10.3762/bjoc.12.216

• of the cycloaddition. If the other possible regioisomer had formed, the 1H NMR spectra would have shown a singlet for the C(4’)H proton. In more detail, the structure of compounds 4 was studied on the example of 4f by COSY, {1H-13C}HSQC, {1H-13C}- and {1H-15N}HMBC NMR experiments. For instance, in

Reactivity studies of pincer bis-protic N-heterocyclic carbene complexes of platinum and palladium under basic conditions

• David C. Marelius,
• Curtis E. Moore,
• Arnold L. Rheingold and
• Douglas B. Grotjahn

Beilstein J. Org. Chem. 2016, 12, 1334–1339, doi:10.3762/bjoc.12.126

• dibasic complex 8. Keywords: NHC; 15N NMR spectroscopy; palladium; platinum; protic N-heterocyclic carbene; Introduction N-Heterocyclic carbenes (NHCs) have been extensively researched for a number of purposes since 1991 when Arduengo first isolated free NHCs [1][2][3]. NHCs as ligands have been known

• and 170 ppm. As for 8-Pt, the 1H NMR spectrum has no peak where the NH peak typically is located, and in the aromatic region there are three peaks. The 13C NMR spectrum thus consists of 9 peaks between 100 and 170 ppm, showing the reappearance of symmetry. 15N chemical shift data give structural

• insight (Table 2), as exemplified by 1–3 [10]. The Δx (difference in 15N shifts for compound x) is near zero for a PNHC (1), maximum for the imidazolyl conjugate base 2, and slightly less for an imidazolyl lithium chloride adduct 3. The δN for the aprotic nitrogen incapable of acid base chemistry (N2

Spiro-fused carbohydrate oxazoline ligands: Synthesis and application as enantio-discrimination agents in asymmetric allylic alkylation

• Jochen Kraft,
• Martin Golkowski and
• Thomas Ziegler

Beilstein J. Org. Chem. 2016, 12, 166–171, doi:10.3762/bjoc.12.18

• )-14 of 9% (Table 1, entry 11). The stereoselectivity of the Pd-catalyzed allylic substitution can be explained via a model for the proposed transition state (Scheme 4). As a consequence of the spiro-fused carbohydrate moiety at the oxazoline ring, exo (15x and 17x) and endo (15n and 17n) diastereomers

• ]. If the nucleophile attacks from the (Si)-face in the fructo-configurated complex 15n product 14 must have the (S)-configuration which is, however, contrary to the observed steroselectivity. Therefore, we suggest 15x to be the preferred isomer for attack by the nucleophile from the (Re)-face which

Recent highlights in biosynthesis research using stable isotopes

• Jan Rinkel and
• Jeroen S. Dickschat

Beilstein J. Org. Chem. 2015, 11, 2493–2508, doi:10.3762/bjoc.11.271

• investigated by fermentation in a 15N-labeled medium and analysis of the resulting product with 13C,15N-HMQC [32]. These applications represent helpful additions to the repertoire for structure elucidation of complex natural products, which can be produced under laboratory conditions in sufficient amounts. Non

The marine sponge Agelas citrina as a source of the new pyrrole–imidazole alkaloids citrinamines A–D and N-methylagelongine

• Christine Cychon,
• Ellen Lichte and
• Matthias Köck

Beilstein J. Org. Chem. 2015, 11, 2029–2037, doi:10.3762/bjoc.11.220

• moiety in compound 2. This structural proposal for citrinamine B (2) was proven by the 1H,13C-HMBC correlations H-2´´ (3.69/3.55 ppm) to C-3´´ (48.6 ppm) and C-15 (178.0 ppm), the 1H,15N-HMBC correlations H-3´´ (2.89/2.80 ppm) to N-1´´ (116 ppm), and the 1H,1H-NOESY correlation H-9/10 (5.95 ppm) to H-1

• (130.2 ppm), and H-17 to C-5 (121.6 ppm) indicated a methylation of the pyrrole nitrogen (Figure 6) which was proven by the 1H,15N-HMBC correlations H-2 to N-1 (159 ppm), H-4 (6.91 ppm) to N-1, and H-17 to N-1. The correlation between the methyl group H-17 and C-6 (158.6 ppm) suggested a linkage with the

• proven by 1H,13C-HMBC correlations, such as H-11 (9.62 ppm) to C-12 (128.0 ppm), C-13 (145.7 ppm), and C-15 (146.6 ppm), H-13 and H-15 to C-11 (146.5 ppm), and H-14 to C-12. The investigation of the 1H,15N-HMBC spectrum of 5 revealed the correlations H-8, H-11, H-14, and H-15 to N-10 (209 ppm) and

The reactions of 2-ethoxymethylidene-3-oxo esters and their analogues with 5-aminotetrazole as a way to novel azaheterocycles

• Marina V. Goryaeva,
• Yanina V. Burgart,
• Marina A. Ezhikova,
• Mikhail I. Kodess and
• Viktor I. Saloutin

Beilstein J. Org. Chem. 2015, 11, 385–391, doi:10.3762/bjoc.11.44

• derivative 6 was not observed even after refluxing for 48 h. Cyclization of compound 6 into tetrazolopyrimidine 7 was performed under prolonged heating without the base. The structure of tetrazolo[1,5-a]pyrimidine 7 was confirmed by IR, 1H, 13C, 2D 1H,13C and 2D 1H,15N HMBC NMR spectra. Thus, the IR spectrum

• carbon. We carried out a series of 2D 1H,15N HMBC experiments for compound 7 varying evolution delay time. In the HMBC spectra correlations between the CH proton (δH = 8.7 ppm) and three 15N atoms at δN = 210.6, 247.4, 306.3 ppm were observed. Based on the published data [22][31], we have assigned these

New highlights of the syntheses of pyrrolo[1,2-a]quinoxalin-4-ones

• Emilian Georgescu,
• Alina Nicolescu,
• Florentina Georgescu,
• Florina Teodorescu,
• Daniela Marinescu,
• Ana-Maria Macsim and
• Calin Deleanu

Beilstein J. Org. Chem. 2014, 10, 2377–2387, doi:10.3762/bjoc.10.248

• -a]quinoxalin-4-ones 4 and 10, and pyrrolo[1,2-a]benzimidazoles 5 were assigned by elemental analysis, IR and NMR spectroscopy. The 1H, 13C and 15N NMR chemical shifts have been unambiguously assigned based on the following 2D NMR experiments: H,H-COSY, H,C-HSQC, H,C-HMBC, H,N-HMBC, H,H-NOESY. In the

• (250 × 4.6) column with a flow rate of 1.0 mL/min. The NMR spectra have been recorded on a Bruker Avance III 400 instrument operating at 400.1, 100.6 and 40.6 MHz for 1H, 13C, and 15N nuclei respectively. Samples were transferred in 5 mm Wilmad 507 NMR tubes and recorded with either a 5 mm multinuclear

• nuclei (CDCl3 referenced at 77.0 ppm), and referenced to liquid ammonia (0.0 ppm) using nitromethane (380.2 ppm) as external standard for 15N nuclei. Unambiguous 1D NMR signal assignments were made based on 2D NMR homo- and heteronuclearcorrelations. H,H-COSY, H,H-NOESY, H,C-HSQC and H,C-HMBC experiments

Syntheses of ¹⁵N-labeled pre-queuosine nucleobase derivatives

• Jasmin Levic and
• Ronald Micura

Beilstein J. Org. Chem. 2014, 10, 1914–1918, doi:10.3762/bjoc.10.199

• pathway of the hypermodified tRNA nucleoside queuosine (Que). The core structure of preQ1 is represented by 7-(aminomethyl)-7-deazaguanine (preQ1 base). Here, we report the synthesis of three preQ1 base derivatives with complementary 15N-labeling patterns, utilizing [15N]-KCN, [15N]-phthalimide, and [15N3

• ]-guanidine as cost-affordable 15N sources. Such derivatives are required to explore the binding process of the preQ1 base to RNA targets using advanced NMR spectroscopic methods. PreQ1 base specifically binds to bacterial mRNA domains and thereby regulates genes that are required for queuosine biosynthesis

• ][7][8]. To explore the binding process of preQ1 base to the RNA and to shed light on the dynamics underpinning this process advanced NMR spectroscopic methods exist for which 15N-labeled preQ1 base derivatives would be highly beneficial. Here, we report efficient routes for the synthesis of three

Synthesis of trifluoromethyl-substituted pyrazolo[4,3-c]pyridines – sequential versus multicomponent reaction approach

• Barbara Palka,
• Angela Di Capua,
• Maurizio Anzini,
• Gyté Vilkauskaité,
• Algirdas Šačkus and
• Wolfgang Holzer

Beilstein J. Org. Chem. 2014, 10, 1759–1764, doi:10.3762/bjoc.10.183

• . Oximes derived from (intermediate) 5-alkynyl-1-phenyl-3-trifluoromethyl-1H-pyrazole-4-carbaldehydes were transformed into the corresponding 1H-pyrazolo[4,3-c]pyridine 5-oxides by silver triflate-catalyzed cyclization. Detailed NMR spectroscopic investigations (1H, 13C, 15N and 19F) were undertaken with

• all obtained products. Keywords: microwave-assisted reactions; multicomponent reactions; NMR (1H; 13C; 15N; 19F); Sonogashira coupling; trifluoromethylpyrazoles; Introduction Fluorine-containing compounds play an important role in medicinal and pharmaceutical chemistry as well as in agrochemistry [1

• investigations In Supporting Information File 1 the NMR spectroscopic data of all compounds treated within this study are indicated. Full and unambiguous assignment of all 1H, 13C, 15N and 19F NMR resonances was achieved by combining standard NMR techniques [32], such as fully 1H-coupled 13C NMR spectra, APT

An experimental and theoretical NMR study of NH-benzimidazoles in solution and in the solid state: proton transfer and tautomerism

• Carla I. Nieto,
• Pilar Cabildo,
• M. Ángeles García,
• Rosa M. Claramunt,
• Ibon Alkorta and
• José Elguero

Beilstein J. Org. Chem. 2014, 10, 1620–1629, doi:10.3762/bjoc.10.168

• .10.168 Abstract This paper reports the 1H, 13C and 15N NMR experimental study of five benzimidazoles in solution and in the solid state (13C and 15N CPMAS NMR) as well as the theoretically calculated (GIAO/DFT) chemical shifts. We have assigned unambiguously the "tautomeric positions" (C3a/C7a, C4/C7 and

• all nuclei have been reported for the three NH-benzimidazoles 1, 2 and 4 [16][17][18][19][20][21]; besides 13C and 15N NMR chemical shifts of 5 have been published [22][23]. Three kinds of calculations have been done: isolated molecules (gas phase), continuous model solvated molecules in DMSO, and

• calculations including DMSO solvent effect (compare eqs. 9 and 10) and also better with trimer B (in turn, slightly better than with trimer A, compare intercept and slopes of eqs. 12 and 13) than with the monomer (eq. 11). iii) Concerning 15N NMR (eqs. 14–21), the R2 values are lower than with 13C NMR. Both

Staudinger ligation towards cyclodextrin dimers in aqueous/organic media. Synthesis, conformations and guest-encapsulation ability

• Malamatenia D. Manouilidou,
• Yannis G. Lazarou,
• Irene M. Mavridis and
• Konstantina Yannakopoulou

Beilstein J. Org. Chem. 2014, 10, 774–783, doi:10.3762/bjoc.10.73

• dissolution of 2 or 3 were observed evidently due to secondary reactions leading to a lower yield for the ligation step. Monomer 4 and dimer 6 displayed a single 31P NMR signal at 35.2 ppm and the correct mass in MALDI–TOF MS. Reaction of 4 with mono(6-15N-amino-6-deoxy)-β-CD under typical amide coupling

• conditions provided the desired dimer 5 (Scheme 3) but only in 10% yield. This product displayed one signal at 35.2 ppm in the 31P NMR spectrum and one at 141.6 ppm in the 15N NMR spectrum, the latter considerably deshielded compared to that of the starting mono(6-15N-amino-6-deoxy)-β-CD at 61.7 ppm, thus

• 3D structure of 4 revealed that the phenyl moieties impose steric restrictions toward the approach of mono(6-15N-amino-6-deoxy)-β-CD. The suggestion of hindrance was supported by the fact that Staudinger ligation using 2 and 3 although very successful with mono[6-(3-azidopropylamino)-6-deoxy]-β-CD

Use of activated enol ethers in the synthesis of pyrazoles: reactions with hydrazine and a study of pyrazole tautomerism

• Denisa Tarabová,
• Stanislava Šoralová,
• Martin Breza,
• Marek Fronc,
• Wolfgang Holzer and
• Viktor Milata

Beilstein J. Org. Chem. 2014, 10, 752–760, doi:10.3762/bjoc.10.70

• unsymmetrical, tautomeric form B was observed (ratio A:B ~ 2:3, Figure 6). The symmetric structure of A can be derived from the fact that in the 1H,15N HMBC spectrum of A there is only one 15N resonance. This resonance consists of residual signals from the incompletely suppressed direct coupling (1J(15N,1H

• second half of the molecule has two equivalent ester moieties and a C=N bond instead of a C=C bond leading to an sp3 hybridized C-atom (δ 54.8 ppm) between the equivalent methyl ester groups. The two different N-atoms in B have 15N chemical shifts of −48.1 ppm (C=N) and −211.7 ppm (=N–NH) (Figure 6

• = 13C [37] and a = −152.0 ± 1.1 ppm , b = −0.946 ± 0.008 for X = 15N [37]. The Gaussian09 [34] software was used for all calculations. Products 5 are formed during reactions in which the proportions of tautomers can theoretically correspond to the proportion of tautomers by the Boltzmann distribution