Enantioselective PCCP Brønsted acid-catalyzed aza-Piancatelli rearrangement

• Gabrielle R. Hammersley,
• Meghan F. Nichol,
• Helena C. Steffens,
• Jose M. Delgado,
• Gesine K. Veits and
• Javier Read de Alaniz

Beilstein J. Org. Chem. 2019, 15, 1569–1574, doi:10.3762/bjoc.15.160

• reaction of the furylcarbinol to generate the oxocarbenium intermediate. Second, by analogy to asymmetric induction in aza-Piancatelli reactions with chiral phosphoric acids, where enantioselectivity has generally been achieved by strategically installing bulky groups on the hydrogen-bonding catalysts, we

• when substituted furylcarbinols were used with either para-iodoaniline (2a) or ortho-aminobenzoic acid (2k, Scheme 2). In every case examined, the ortho-aminobenzoic acid gave higher selectivity compared to the corresponding para-iodoaniline, which supports the importance of the additional hydrogen

• bonding capability of the carboxylic acid group. In contrast, with the exception of 7p and 7q, a lower yield was obtained when ortho-aminobenzoic acid was used. Presumably, this decrease in efficiency is due to the increased steric bulk on the aniline, which slows the initial nucleophilic attack on the

Molecular basis for the plasticity of aromatic prenyltransferases in hapalindole biosynthesis

• Takayoshi Awakawa and
• Ikuro Abe

Beilstein J. Org. Chem. 2019, 15, 1545–1551, doi:10.3762/bjoc.15.157

• , an X-ray crystallization analysis was conducted. The apo structure of AmbP1 was solved at 2.35 Å, and it adopted an ABBA fold [4][5][13]. Interestingly, the apo structure unusually includes the Mg2+ ion in a position nearby the β-barrel, stabilized by hydrogen bonding with N41, E63, and D65 (Figure

• distance from C-1 of GSPP to C-3 of 1 (Figure 4B, c: 4.6 Å) became closer than that to C-2 of 1 (Figure 4B, d: 5.4 Å). Importantly, an additional Mg2+ ion (Figure 3C, Mg-2) appeared in the active site close to the isonitrile of 1, stabilized by the hydrogen bonding with D172, T173, G208, and E209 (Figure

• ]. The prenyl acceptors, HU and HA, were both surrounded by hydrophobic amino acids, including A44, A102, W117, L119, L259, V284, F288, and M291 [14], and the position of HU was additionally stabilized by hydrogen bonding between the N-1 of HU and E207 (Figure 5A). Remarkably, the terpenoid moieties of

A heteroditopic macrocycle as organocatalytic nanoreactor for pyrroloacridinone synthesis in water

• Piyali Sarkar,
• Sayan Sarkar and
• Pradyut Ghosh

Beilstein J. Org. Chem. 2019, 15, 1505–1514, doi:10.3762/bjoc.15.152

• of macrocycles with multiple functional groups has been employed as alternative templates to induce the organic environment for catalysis via multiple weak interactions viz. π–π stacking, hydrogen bonding, etc. [25][26][27][28][29]. At the same time, several efforts have been made to develop

2,3-Dibutoxynaphthalene-based tetralactam macrocycles for recognizing precious metal chloride complexes

• Li-Li Wang,
• Yi-Kuan Tu,
• Huan Yao and
• Wei Jiang

Beilstein J. Org. Chem. 2019, 15, 1460–1467, doi:10.3762/bjoc.15.146

• hydrogen bonds to recognize guests with hydrogen-bonding acceptors. Precious metal chloride complexes were found to be complexed by 1. Obvious chemical shifts in the 1H NMR spectra (Figure 3) were observed for H6 and amide NH protons when adding one equivalent of the tetrabutylammonium (TBA+) salt of AuCl4

• smaller than that in the presence of one equivalent of TBA[AuCl4] (Figure 3), although they have rather similar binding affinities. This may be due to a different extent hydrogen bonding is involved in diverse complexes and other non-covalent interactions may contribute more in the cases of (TBA)2[PtCl4

Reaction of oxiranes with cyclodextrins under high-energy ball-milling conditions

• László Jicsinszky,
• Federica Calsolaro,
• Katia Martina,
• Fabio Bucciol,
• Maela Manzoli and
• Giancarlo Cravotto

Beilstein J. Org. Chem. 2019, 15, 1448–1459, doi:10.3762/bjoc.15.145

• cyclodextrins (CDs, cyclic α(1->4)-linked glucopyranosides) is always a difficult task, particularly when the attached moiety is prone to further derivatisation. In many cases, statistical (random) substitution results in essential changes in the hydrogen bonding systems of the cyclodextrin hydroxy rims, and is

One-pot activation–alkynylation–cyclization synthesis of 1,5-diacyl-5-hydroxypyrazolines in a consecutive three-component fashion

• Christina Görgen,
• Katharina Boden,
• Guido J. Reiss,
• Walter Frank and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2019, 15, 1360–1370, doi:10.3762/bjoc.15.136

• to spectroscopic assignment the structure of 6a has now been corroborated by an X-ray structure analysis showing infinite chains of molecules 6a formed by intermolecular hydrogen bonding between the pyrazole N1 and the carbonyl O1 (Figure 3) [53]. The first assumption was that the tentative

• analyses. Additionally, the structure was corroborated by an X-ray structure analysis of compound 5r showing dimers held together by inter- and intramolecular hydrogen bonding (Figure 5) [53]. The three-component synthesis allows addressing three points of diversity and especially for the hydrazide

• ) and antibacterial activity (center and right). ORTEP plot of 5-benzoyl-3-phenyl-1H-pyrazole (6a) (thermal ellipsoids at 30% probability); the direction of intermolecular N−H···O hydrogen bonding is indicated by dashed lines. Ellipsoid plot of 1-Boc-5-benzoyl-5-hydroxypyrazoline 5a. ORTEP plot and

Formation of an unexpected 3,3-diphenyl-3H-indazole through a facile intramolecular [2 + 3] cycloaddition of the diazo intermediate

• Andrew T. King,
• Hugh G. Hiscocks,
• Lidia Matesic,
• Mohan Bhadbhade,
• Roger Bishop and
• Alison T. Ung

Beilstein J. Org. Chem. 2019, 15, 1347–1354, doi:10.3762/bjoc.15.134

• Pauling-type hydrogen bonding, and therefore weaker attractions must be used in the crystal packing. Its interaction between the methoxy and diazo functionalities is uncommon, though entirely reasonable in the context of weak hydrogen bonding [14]. The presence of close C–H···H–C contacts in this

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

• coordinated to Ni in more Lewis acidic equatorial position, whereas the nitroalkene is positioned in apical by avoiding the steric repulsion of benzyl groups (TS2-I and 2-II vs TS1-I and 1-II, Scheme 2). Additional hydrogen bonding between the hydrogen atom of the amino group and the oxygen atom of the

Bambusuril analogs based on alternating glycoluril and xylylene units

• Tomáš Lízal and
• Vladimír Šindelář

Beilstein J. Org. Chem. 2019, 15, 1268–1274, doi:10.3762/bjoc.15.124

• ; supramolecular chemistry; Introduction Macrocycles consisting of urea building blocks play an important role in supramolecular chemistry [1]. Urea N–H motifs provide macrocycles with the ability to act as anion receptors due to the stabilizing effect of N–H···anion hydrogen bonding [2][3][4]. Furthermore, the

• urea groups can participate in intermolecular hydrogen bonding resulting in the formation of tubular [5][6][7] or gel-like [8] structures. Ureas lacking of N–H hydrogen atoms such as ethyleneureas, glycolurils, and biotin are also important building blocks of macrocyclic receptors such as cucurbiturils

• [9] and hemicucurbiturils [10]. Bambus[6]urils are a special case of hemicucurbiturils, which comprise six glycoluril units connected by six methylene bridges within their structure [11][12]. Due to their hydrophobic cavity with 12 methine hydrogen atoms available for hydrogen bonding, bambus[6]urils

Self-assembly behaviors of perylene- and naphthalene-crown macrocycle conjugates in aqueous medium

• Xin Shen,
• Bo Li,
• Tiezheng Pan,
• Jianfeng Wu,
• Yangxin Wang,
• Jie Shang,
• Yan Ge,
• Lin Jin and
• Zhenhui Qi

Beilstein J. Org. Chem. 2019, 15, 1203–1209, doi:10.3762/bjoc.15.117

• through hydrogen bonding and metal ion coordination in nonpolar solvents [66][67][68]. Compared with NDI, PDI has more aromatic rings to generate stronger intermolecular π−π stacking, leading to molecular aggregates more easily, and these aggregates or supramolecular assemblies can give rise to desirable

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls

• Dong-Hao Li and
• Bradley D. Smith

Beilstein J. Org. Chem. 2019, 15, 1086–1095, doi:10.3762/bjoc.15.105

• enables them to be effective hosts for a wide range of guest molecules including organic biscarbonyl derivatives, near-infrared dyes, acenes, precious metal halide complexes, trimethylammonium ion-pairs, and saccharides. Keywords: fluorescent dye; host–guest chemistry; hydrogen bonding; hydrophobic

• the central cavity. In organic solvents, hydrogen bonding with the four tetralactam NH residues is the dominant interaction that drives encapsulation of complementary guests, with aromatic stacking as a secondary contributor [23][24][25]. In water, the thermodynamic importance of these non-covalent

• factors is reversed; hydrogen bonding is relatively weak and strong guest association occurs when hydrophobic sections of a complementary guest are able to contact the hydrophobic interior surfaces of the two aromatic sidewalls [26]. The first macrocycle system in Scheme 1 to be studied in detail was

Fabrication, characterization and adsorption properties of cucurbit[7]uril-functionalized polycaprolactone electrospun nanofibrous membranes

• Changzhong Chen,
• Fengbo Liu,
• Xiongzhi Zhang,
• Zhiyong Zhao and
• Simin Liu

Beilstein J. Org. Chem. 2019, 15, 992–999, doi:10.3762/bjoc.15.97

• ][23][24]. Through hydrophobic effects, ion–dipole interactions, and/or hydrogen bonding, CB[n]s show selective molecular recognition properties towards cationic and neutral guests [25][26]. In the last two decades, CB[n]s have been used for a variety of applications including supramolecular catalysis

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