Catalytic asymmetric oxo-Diels–Alder reactions with chiral atropisomeric biphenyl diols

• Chi-Tung Yeung,
• Wesley Ting Kwok Chan,
• Wai-Sum Lo,
• Ga-Lai Law and
• Wing-Tak Wong

Beilstein J. Org. Chem. 2019, 15, 955–962, doi:10.3762/bjoc.15.92

• hydrogen bonding organocatalyst for the reaction between 1-dimethylamino-3-tert-butyldimethylsilyloxy-1,3-butadiene (Rawal’s diene) and aldehydes with excellent enantioselectivities (aromatic aldehyde: up to 86–98% ee) in 2003 [27]. Activation via a single-point hydrogen bond between one of the hydroxy

• groups of the TADDOL and the carbonyl oxygen of the aldehyde was proposed to be a crucial factor for the success of this organocatalyst in the reaction. Two years later, they reported another efficient diol-based hydrogen bonding organocatalyst, BAMOL, for catalyzing the same oxo-DA reactions with a

• library of aldehydes (aromatic: 97–99% ee; aliphatic: 84–98% ee) [28]. Thereafter, many different kinds of hydrogen bonding-based organocatalysts have been developed for oxo-DA reactions [29][30][31][32][33][34][35]. One kind of organocatalyst in particular, which is based on an oxazoline template with

Halogen bonding and host–guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests

• Fangfang Pan,
• Mohadeseh Dashti,
• Michael R. Reynolds,
• Kari Rissanen,
• John F. Trant and
• Ngong Kodiah Beyeh

Beilstein J. Org. Chem. 2019, 15, 947–954, doi:10.3762/bjoc.15.91

• type of directional non-covalent interaction, is regarded as the “long lost brother” of hydrogen bonding (HB) [6][7]. Although XB in many aspects is very similar to HB, and in most cases not as strong as classical HB, the character of XB, such as hydrophobicity, adjustability, or softness, allows these

• yellow cloud. (a) The halogen bonding (blue broken lines), hydrogen bonding (red broken lines) and the host–guest effect (water molecules in CPK, and the cavity space in transparent yellow cloud) in Water@2&DIOFB; (b) The halogen bonded polymer. Water molecules in CPK mode and all the other in ball-and

Mechanochemistry of supramolecules

• Anima Bose and
• Prasenjit Mal

Beilstein J. Org. Chem. 2019, 15, 881–900, doi:10.3762/bjoc.15.86

• capsule 40 formed through hydrogen-bonding and the cavity was found to be able to encapsulate different organic molecules such as alkanes, acids, amines, etc. The encapsulation of a [2.2]paracyclophane in the cage was achieved by ball milling at 30 Hz (Figure 22) and the host–guest product 40 was verified

• chemistry reactions, as it relies on soft force [97][98] or non-covalent interactions [2] such as hydrogen bonding [99], cation–π [100][101][102], anion–π [103], hydrophobic effect [104][105], halogen bonding [106][107][108][109], etc. As enzymes are structurally complex entities and are difficult to modify

Efficient synthesis of pyrazolopyridines containing a chromane backbone through domino reaction

• Razieh Navari,
• Saeed Balalaie,
• Saber Mehrparvar,
• Fatemeh Darvish,
• Frank Rominger,
• Fatima Hamdan and
• Sattar Mirzaie

Beilstein J. Org. Chem. 2019, 15, 874–880, doi:10.3762/bjoc.15.85

• . The use of a protic solvent seems to be essential for the progress of the reaction and may related to the dipole moment and also the hydrogen-bonding ability of protic solvents. The spectroscopic data confirmed the formation of 4a. The X-ray crystallographic data of compound 4a confirmed the structure

• molecules based on the pyrazolopyridine framework. ORTEP Structure of compound 4a and intermolecular hydrogen bonding; the ellipsoid probability level of each ORTEP diagram is 50%. Structures of synthesized pyrazolopyridines 4a–m. Reaction conditions: 3-formylchromone derivatives (1 mmol), primary amine

Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines

• Camila B. Francisco,
• Cleverton S. Fernandes,
• Ulisses Z. de Melo,
• Roberto Rittner,
• Gisele F. Gauze and
• Ernani A. Basso

Beilstein J. Org. Chem. 2019, 15, 818–829, doi:10.3762/bjoc.15.79

• halogen size. Instead, the equilibrium is influenced by solute–solvent hydrogen bonding with the hydroxy group. Besides the classical effects, interactions such as hyperconjugation has been pointed out as relevant in several studies involving cyclohexane derivatives [4][12][15][16][17][18][19][20]. Since

Solid-phase synthesis of biaryl bicyclic peptides containing a 3-aryltyrosine or a 4-arylphenylalanine moiety

• Iteng Ng-Choi,
• Àngel Oliveras,
• Lidia Feliu and
• Marta Planas

Beilstein J. Org. Chem. 2019, 15, 761–768, doi:10.3762/bjoc.15.72

• ][2][10][11][12][13][14]. The most frequently used are the formation of an amide bond between the N- and the C-terminus and the cyclization involving the side chain of two amino acids. The latter is considered more convenient, because it does not interfere on hydrogen bonding between the N- and C

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

• Grzegorz Mlostoń,
• Małgorzata Celeda,
• Katarzyna Urbaniak,
• Marcin Jasiński,
• Vladyslav Bakhonsky,
• Peter R. Schreiner and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2019, 15, 497–505, doi:10.3762/bjoc.15.43

• skeleton appeared in a narrow range at 89.0–86.9 ppm. Unexpectedly, in the case of 7e, the same procedure led to the final, crystalline product as a hydrochloride. Apparently, hydrogen bonding in this molecule is strong enough to bind an HCl molecule, which cannot be removed by treatment with solid NaHCO3

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

• solvent properties such as viscosity or hydrogen bonding. Interestingly, purine class compound 8c showed a dual-fluorescence character in the solvents of higher polarity (DMSO, MeCN) arising from the locally excited and charge transfer excited states, however, dual-fluorescence was not evident for the 7

LCST phase behavior of benzo-21-crown-7 with different alkyl chains

• Yan Deng,
• Xing Li,
• Qiao Zhang,
• Zheng Luo,
• Chengyou Han and
• Shengyi Dong

Beilstein J. Org. Chem. 2019, 15, 437–444, doi:10.3762/bjoc.15.38

• of linkage becomes more profound, the weak hydrogen bonding between water molecules and crown ethers are attenuated or destroyed, which will further prevent the aggregation of crown ethers and prohibit the occurrence of LCST. By the analyses and comparisons of the LCST behaviors of 3a–e and 5a–e, the

Synthesis of nonracemic hydroxyglutamic acids

• Dorota G. Piotrowska,
• Iwona E. Głowacka,
• Andrzej E. Wróblewski and
• Liwia Lubowiecka

Beilstein J. Org. Chem. 2019, 15, 236–255, doi:10.3762/bjoc.15.22

• additional substituents, tuning the conformational flexibility of analogues and introducing groups capable of hydrogen bonding. Crystallographic data obtained for glutamate receptors [13][14][15] showed complex set of atoms interacting electrostatically and through hydrogen bonds and the conclusions from

• ][44]. Natural occurrence as well as possibilities of glutamate-like biological activity modulated by additional hydrogen bonding with hydroxy groups inspired the interest in the synthesis of stereoisomers of hydroxyglutamic acids 2–4 (Figure 2). Since they contain two or three stereogenic centers

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

• Falco Fox,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2019, 15, 167–186, doi:10.3762/bjoc.15.17

• attractive target molecules due their hydrogen-bonding capabilities [1][2][3][4][5][6]. Two synthetic routes are available for syntheses of organosilanediols: If diphenylsilanes are used as building blocks, this route is well suited for syntheses of silanediols with electrophilic functions. In this case, the

• ], (thio)ureas [30][31] and phosphoric acid derivatives [27]. Cyclodiphosph(V)azanes [32][33][34][35] and silanediols [1][28][36] are two new hydrogen bonding scaffolds for anion recognition [37] and ion-pair catalysis [6][38]. Since Kondo et al. established silanediol 1 [39] as HBD for anion recognition

• chloride ion is abstracted from 10 and binds via hydrogen bonding to the catalyst (Scheme 6) [45][47]. This leads to an ion pair [cat•Cl]− and [isoquinolinium cation]+ (Scheme 6). The nucleophilic silyl ketene acetal reacts with the [isoquinolinium cation]+ and forms the C–C bond, yielding product 12

Ammonium-tagged ruthenium-based catalysts for olefin metathesis in aqueous media under ultrasound and microwave irradiation

• Łukasz Gułajski,
• Andrzej Tracz,
• Katarzyna Urbaniak,
• Stefan J. Czarnocki,
• Michał Bieniek and
• Tomasz K. Olszewski

Beilstein J. Org. Chem. 2019, 15, 160–166, doi:10.3762/bjoc.15.16

• Marcus postulated a trans-phase hydrogen bonding from water OH groups to H-bond acceptor sites of organic reactants contributing to a stabilisation of organic transition states enables the on-water catalysis [77]. Ben-Amotz et al. demonstrated that the effect of the water OH groups depends either on the

Computational characterization of enzyme-bound thiamin diphosphate reveals a surprisingly stable tricyclic state: implications for catalysis

• Ferran Planas,
• Michael J. McLeish and
• Fahmi Himo

Beilstein J. Org. Chem. 2019, 15, 145–159, doi:10.3762/bjoc.15.15

• hydrogen bonding distance of the C2 of the thiazolium ring [9][10][11][12][13][14]. While the importance of the catalytically critical ylide was readily recognized, obtaining evidence for the participation of the 4′-amino group and the imino tautomer IP proved more challenging. Initially, model compounds

• ) were obtained using DFT methods, employing a model of the cofactor along with the hydrogen-bonding carboxylate moiety [23]. Subsequently, a similar approach was used to characterize the nucleophilicity of the N1′ and N4′ centers [24]. In many cases, rather than simply focus on the cofactor

• position regardless of the state of the cofactor. A superposition with the crystal structure without substrate (PDB 1BFD) shows that the model calculations reproduce very well the position of this water (see Supporting Information File 1), even though the hydrogen-bonding pattern of the water molecule

Adhesion, forces and the stability of interfaces

• Robin Guttmann,
• Johannes Hoja,
• Christoph Lechner,
• Reinhard J. Maurer and
• Alexander F. Sax

Beilstein J. Org. Chem. 2019, 15, 106–129, doi:10.3762/bjoc.15.12

• large variety of WMIs. To some of them, special names are assigned, such as hydrogen bonding or hydrophobic interactions. In chemistry, these WMIs are frequently used as if they were basic interaction types. For a long time, dispersion was largely ignored in chemistry, attractive intermolecular

• their different flavors. Hydrogen bonding is a typical WMI. As such, it is composed of the abovementioned basic interactions, each having its own strength and range. Nevertheless, it is common practice in chemistry to speak about hydrogen bonding as if it was indeed a genuine basic interaction rather

• than a composed interaction. Instead of stressing the different compositions of the basic interactions, chemists speak of strong, moderate or weak hydrogen bonding [3]; sometimes even further divisions are made [4]. Hydrogen bonding was introduced nearly 100 years ago to explain the stabilization of

A simple and effective preparation of quercetin pentamethyl ether from quercetin

• Jin Tatsuzaki,
• Tomohiko Ohwada,
• Yuko Otani,
• Reiko Inagi and
• Tsutomu Ishikawa

Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291

• University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0013, Japan 10.3762/bjoc.14.291 Abstract Among the five hydroxy (OH) groups of quercetin (3,5,7,3',4'-pentahydroxyflavone), the OH group at 5 position is the most resistant to methylation due to its strong intramolecular hydrogen bonding with the

• -methylation is difficult because the OH group at 5 position is resistant to alkylation due to its strong intramolecular hydrogen bonding with the carbonyl group at 4 position. Indeed, inconsistent experimental results have been reported in the literature; incomplete methylation occurred in some cases [24][34

• (run 1 in Table 2, see Supporting Information File 1). The tetramethyl ether 4 showed a lower-field-shifted signal at 12.64 ppm in the 1H NMR spectrum (see Supporting Information File 2), due to strong intramolecular hydrogen-bonding of the OH group at 5 position with the carbonyl group at 4 position

1,8-Bis(dimethylamino)naphthyl-2-ketimines: Inside vs outside protonation

• A. S. Antonov,
• A. F. Pozharskii,
• P. M. Tolstoy,
• A. Filarowski and
• O. V. Khoroshilova

Beilstein J. Org. Chem. 2018, 14, 2940–2948, doi:10.3762/bjoc.14.273

• proton sponge moiety to occupy the in,out-conformation [14] with the 1-NMe2 group participating in NHN intramolecular hydrogen bonding with the C=NH2+ group (Scheme 8). Indeed, in the case of 7b’, which contains three OMe groups, we have found direct evidence of this process: the 1-NMe2 group signal

• 10 (Scheme 8, right), which is out-protonated due to steric reasons [15]. In refs. [15][16][17] it was shown that hydrogen bonding to an out-inverted NMe2 group without the proton transfer does not noticeably change the chemical shift of methyl protons. Thus, in the case of 7b’, the chemical shift at

Nucleoside macrocycles formed by intramolecular click reaction: efficient cyclization of pyrimidine nucleosides decorated with 5'-azido residues and 5-octadiynyl side chains

• Jiang Liu,
• Peter Leonard,
• Sebastian L. Müller,
• Constantin Daniliuc and
• Frank Seela

Beilstein J. Org. Chem. 2018, 14, 2404–2410, doi:10.3762/bjoc.14.217

• ellipsoids are drawn at the 50% probability level and H-atoms are shown as small spheres of arbitrary size. Hydrogen bonds are shown as dashed lines. The crystal packing of 8 shows the intramolecular hydrogen-bonding network (projection parallel to the x-axis). N- and S-conformation for cyclonucleoside 8. B

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

• residual value (Table 1). Conceivably, this may be due to intermolecular hydrogen bonding with the solvent or other alcohol molecules in the concentrated solution. In fact, including a methanol solvent molecule as a hydrogen-bond donor in the DFT calculation will shift the δcalc in the right direction for

Tetrathiafulvalene – a redox-switchable building block to control motion in mechanically interlocked molecules

• Hendrik V. Schröder and
• Christoph A. Schalley

Beilstein J. Org. Chem. 2018, 14, 2163–2185, doi:10.3762/bjoc.14.190

• lasso, a structural motif which was also recently found in nature for peptides with high antibacterial efficacy [71]. In 12, the TTF molecule is not implemented in the thread but in the wheel component. In the neutral state, strong hydrogen bonding between the crown ether wheel and the dialkylammonium

• hydrogen bonding. Detailed electrochemical measurements and digital simulations revealed the ring still to be bound to the ammonium station in the TTF●+ state. However, after double oxidation a wheel distribution of 1:1 between the ammonium and the isoxazole station was found indicating a dynamic motion

• Figure 27b), donor–acceptor interactions and hydrogen bonding generate a neutral TTF dimer that is surrounded by cofacially oriented bipyridinium units [112]. The intertwined structure is locked by formation of platinum(II)–pyridine coordination bonds. Interestingly, the doubly interlocked catenane

A switchable [2]rotaxane with two active alkenyl groups

• Xiu-Li Zheng,
• Rong-Rong Tao,
• Rui-Rui Gu,
• Wen-Zhi Wang and
• Da-Hui Qu

Beilstein J. Org. Chem. 2018, 14, 2074–2081, doi:10.3762/bjoc.14.181

• a ΔδH3 = 0.51 ppm due to the association with the DB24C8 macrocycle through hydrogen bonding. All the evidences reveal that the functionalized macrocycle migrated from the DBA recognition site to the amide station when an external base was added to the solution of rotaxane R1. Then, 3 equiv

Synthesis and supramolecular self-assembly of glutamic acid-based squaramides

• Juan V. Alegre-Requena,
• Marleen Häring,
• Isaac G. Sonsona,
• Alex Abramov,
• Eugenia Marqués-López,
• Raquel P. Herrera and
• David Díaz Díaz

Beilstein J. Org. Chem. 2018, 14, 2065–2073, doi:10.3762/bjoc.14.180

• asymmetric catalysis and molecular recognition [5][6]. Besides, squaramides present a dual ability to recognize anions and cations through hydrogen bonding interactions, acting as ion sensors and transmembrane anion transporters [7]. This property has been crucial for the development of new drugs [8][9

• shifts for characteristic bands such as C=O stretching (≈1735 cm−1), and N–H stretching ≈2867–3000 cm−1 (Supporting Information File 1, Figure S2). This suggests that the gelator may also be aggregated in solution, at least to some extend, via similar hydrogen-bonding interactions than in the gel state

• . In contrast, the spectrum of the xerogel, prepared by freeze-drying the corresponding organogel, revealed a red shift (lower frequency) of the above-mentioned stretching bands compared to solid 3 (C=O Δν ≈5 cm−1; N–H Δν ≈70 cm−1), which is an indication of increased hydrogen-bonding. Characterization

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• the epoxides of the graphene-family material. In a coupling with the inclusion of graphene-family material and amine hydrohalide some reactions or transformations may occur, but they are based on electrostatic adsorption or hydrogen bonding [23], rather than on covalent modification. If formation of

• inner salt or hydrogen bonding, as the presence of absorption bands located in 1610–1587 cm−1 (asymmetric vibrations of C=O of –COO− and N–H of NH3+) and 1475–1385 cm−1 (symmetric vibrations of C=O of –COO− and N–H of NH3+) ranges indeed implies. The absorption band located at 3016 cm−1, interestingly

• and hydrogen bonding-dependent adsorption of glucose on the RGO surface results in a shift of the absorption bands coming from the C=O of RGO (from 1724 cm−1 to 1735 cm−1). Another consideration is that this process further influences the obtained material’s morphology, properties and thermal

A self-assembled photoresponsive gel consisting of chiral nanofibers

• Lei Zou,
• Dan Han,
• Zhiyi Yuan,
• Dongdong Chang and
• Xiang Ma

Beilstein J. Org. Chem. 2018, 14, 1994–2001, doi:10.3762/bjoc.14.174

• by three-dimensional networks through self-assembly have drawn significant attention in the past decades. They are normally fabricated by means of noncovalent intermolecular interactions [3], such as π–π stacking, hydrogen bonding, van der Waals forces, hydrophobic, electrostatic, host–guest and

• is used as a candidate to form a new chiro-optical system [30][36][37][38][39][40][41]. Ureidopyrimidinone (UPy), as a connection site, is also introduced to make quadruple hydrogen bonding [42][43][44]. The structure and schematic representation of 3 are shown in Figure 1. The possible assembly

• Discussion The monomolecular compound 3 can be easily synthesized in 3 steps. The compound has the necessary features for gel formation. The quadruple hydrogen bonding created by UPy moieties is quite stable in nonpolar solvents. Therefore, the molecule can easily assemble into dimers. Then, the trans

Synthesis of new p-tert-butylcalix[4]arene-based polyammonium triazolyl amphiphiles and their binding with nucleoside phosphates

• Vladimir A. Burilov,
• Guzaliya A. Fatikhova,
• Mariya N. Dokuchaeva,
• Ramil I. Nugmanov,
• Diana A. Mironova,
• Pavel V. Dorovatovskii,
• Victor N. Khrustalev,
• Svetlana E. Solovieva and
• Igor S. Antipin

Beilstein J. Org. Chem. 2018, 14, 1980–1993, doi:10.3762/bjoc.14.173

• nucleotides must possess selectivity towards these anions. From this point of view, nucleotide receptors based on polyammonium cations are of great demand because the electrostatic interactions of such polyammonium systems and negatively charged phosphates are strong. Hydrogen bonding [8] and π-stacking

• macrocycles 10a, 12a,b (Figure 3) can be rationalized in terms of the binding properties of the investigated nucleotides. Moreover, the presence of intramolecular hydrogen bonding (Figure 4a and b) can explain the protonation of only one nitrogen atom despite the close protonation constants of both primary

A pyridinium/anilinium [2]catenane that operates as an acid–base driven optical switch

• Sarah J. Vella and
• Stephen J. Loeb

Beilstein J. Org. Chem. 2018, 14, 1908–1916, doi:10.3762/bjoc.14.165

• )ethane recognition site [18]. In particular, the significant downfield shifts observed for ethylene protons s and t from 5.30 ppm in 74+ to 5.56 ppm for [8DB24C8]6+ as well as u and r, the ortho pyridinium protons, from 9.04 ppm in 74+ to 9.31 ppm for [8DB24C8]6+ are characteristic of hydrogen-bonding to