Evaluating the halogen bonding strength of a iodoloisoxazolium(III) salt

• Dominik L. Reinhard,
• Anna Schmidt,
• Marc Sons,
• Julian Wolf,
• Elric Engelage and
• Stefan M. Huber

Beilstein J. Org. Chem. 2024, 20, 2401–2407, doi:10.3762/bjoc.20.204

• , halogen bonding [I1···Br1 = 3.0610(5) Å, 80% of Σr, and C8–I1···Br1 = 171.67(9)°] and hydrogen bonding were found [H2···Br1 = 2.7991(4) Å, 95% of Σr, C2···Br1 = 3.545(4) Å, 100% of Σr and C2–H2···Br1 = 136.1(2)°]. On the other axis, no ortho proton is present, so only XB is observed [I1···Br1 = 3.2023(5

• ). Halogen bonding dimer found in the crystal structure of 7Br. Ellipsoids are shown at 50% probability (carbon: grey, nitrogen: blue, oxygen: red, bromine: orange, iodine: purple) and hydrogen atoms are shown in standard ball-and-stick model (white). Halogen and hydrogen bonding is indicated dashed. 1H NMR

Asymmetric organocatalytic synthesis of chiral homoallylic amines

• Nikolay S. Kondratyev and
• Andrei V. Malkov

Beilstein J. Org. Chem. 2024, 20, 2349–2377, doi:10.3762/bjoc.20.201

• the asymmetric addition of organoboron reagents to imines (Scheme 3). An intermolecular hydrogen bonding between a non-rigid organocatalyst and a non-rigid substrate was shown to play a key role in assembling a configurationally stable transition structure. As a result, this approach unveiled the

Stereoselective mechanochemical synthesis of thiomalonate Michael adducts via iminium catalysis by chiral primary amines

• Michał Błauciak,
• Dominika Andrzejczyk,
• Błażej Dziuk and
• Rafał Kowalczyk

Beilstein J. Org. Chem. 2024, 20, 2313–2322, doi:10.3762/bjoc.20.198

• catalysis with hydrogen bonding units has been essential for achieving high reactivity and enantioselectivities [21][22]. Additionally, the reactivity of the nucleophilic addition is influenced by substitutions near the electron-poor double bond. This approach requires 30 mol % of catalyst and a reaction

• proved ineffective in facilitating the Michael addition of bisthiomalonates to conjugated ketones, whereas DABCO enabled the formation of desired products under mild conditions [30]. However, reports of highly stereoselective protocols utilizing hydrogen bonding catalysis have mainly focused on

• -based catalytic system for the highly stereoselective addition of various bisthiomalonates to chalcones and dienones [29]. While recognizing the potential for greater selectivity enhancement and time savings with ball milling, hydrogen-bonding catalysis was effective only with aromatic enones, yielding

Hydrogen-bond activation enables aziridination of unactivated olefins with simple iminoiodinanes

• Phong Thai,
• Lauv Patel,
• Diyasha Manna and
• David C. Powers

Beilstein J. Org. Chem. 2024, 20, 2305–2312, doi:10.3762/bjoc.20.197

• iminoiodinanes for the metal-free aziridination of unactivated olefins. 1H NMR and cyclic voltammetry (CV) studies indicate that hydrogen-bonding between HFIP and the iminoiodinane generates an oxidant capable of direct NGT to unactivated olefins. Stereochemical scrambling during aziridination of 1,2

• at 5.52 ppm with a FWHM = 56.6 Hz (Scheme 4a). This resonance was broader and more downfield than that of free HFIP in CD3CN (5.41 ppm with FWHM = 5.0 Hz), suggesting a hydrogen bonding interaction between HFIP and 2c, and similar observations were also reported for the hydrogen bonding between HFIP

• (denoted by asterisk *) of HFIP in the presence of iminoiodinane 2c suggesting hydrogen bonding observed in 1H NMR spectra (CD3CN) of: 8.0 mM 2c with no HFIP (blue line), 8.0 mM 2c with 32 mM HFIP (green line), 4.0 mM of 4-(trifluoromethyl)benzenesulfonamide with 32 mM HFIP (purple line), only 32 mM HFIP

Factors influencing the performance of organocatalysts immobilised on solid supports: A review

• Zsuzsanna Fehér,
• Dóra Richter,
• Gyula Dargó and
• József Kupai

Beilstein J. Org. Chem. 2024, 20, 2129–2142, doi:10.3762/bjoc.20.183

• adsorbed onto the support surface through weaker intermolecular forces, such as van der Waals forces and hydrogen bonding. Ionic catalysts form ionic bonds or those that can be ionised under immobilisation conditions. Encapsulation involves physically trapping the catalyst within the pores or cavities of

• catalyst can easily leach into the solution as it reaches equilibrium between the absorbed species on the surface and the solubilised species. To improve the stability of the supported catalyst, it is important to modify the catalyst and support to enable hydrogen bonding. This method can also bring the

• organocatalyst [113], reactants [114], product [115] or solvent [116] can significantly impact catalytic activity. These interactions often manifest in various forms of adsorption: physisorption, involving forces like van der Waals interactions and hydrogen bonding, or chemisorption, which may involve ionic or

Solvent-dependent chemoselective synthesis of different isoquinolinones mediated by the hypervalent iodine(III) reagent PISA

• Ze-Nan Hu,
• Yan-Hui Wang,
• Jia-Bing Wu,
• Ze Chen,
• Dou Hong and
• Chi Zhang

Beilstein J. Org. Chem. 2024, 20, 1914–1921, doi:10.3762/bjoc.20.167

• substrate 1c may act as an electrophilic center, forming a C–O bond with the alkenyl group to give the isochromen-1-one oxime product 2c'. When wet HFIP was used as the solvent, the reaction followed a different pathway. HFIP, a strong hydrogen bonding donor [26][27][28], interacts with the amide moiety of

The Groebke–Blackburn–Bienaymé reaction in its maturity: innovation and improvements since its 21st birthday (2019–2023)

• Cristina Martini,
• Muhammad Idham Darussalam Mardjan and
• Andrea Basso

Beilstein J. Org. Chem. 2024, 20, 1839–1879, doi:10.3762/bjoc.20.162

• . Sashidhara et al. reported no conversion, while Liu et al. reported a 58% yield of the GBB product, postulating the ability of ethylene glycol to function as an activator (through hydrogen bonding) and a facilitator of proton transfer. After this discovery, ethylene glycol has never been employed in GBB

• significantly more active than 9, owing to higher rigidity and the correct position of the ortho H atoms in close proximity to the σ-holes on the I atom. The authors demonstrated that hydrogen bonding between H in ortho position of 8 and both O atom of aldehyde and N atom of imine significantly increased the

Supramolecular assemblies of amphiphilic donor–acceptor Stenhouse adducts as macroscopic soft scaffolds

• Ka-Lung Hung,
• Leong-Hung Cheung,
• Yikun Ren,
• Ming-Hin Chau,
• Yan-Yi Lam,
• Takashi Kajitani and
• Franco King-Chi Leung

Beilstein J. Org. Chem. 2024, 20, 1590–1603, doi:10.3762/bjoc.20.142

• stronger fatigue effect was observed in the photoisomerization of DA7 and DA6, this might be attributed to stabilization through hydrogen bonding and a favored cyclized-isomer in polar solvents. The increased alkyl linker length of DA10 and DA11 provided an improved photostability compared to DA7 and DA6

Regio- and stereochemical stability induced by anomeric and gauche effects in difluorinated pyrrolidines

• Ana Flávia Candida Silva,
• Francisco A. Martins and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2024, 20, 1572–1579, doi:10.3762/bjoc.20.140

• systems [5]. This conformational preference is attributed to an electrostatic gauche effect, where an attractive NH2+∙∙∙Fδ− interaction reinforces the well-known hyperconjugative gauche effect. Additionally, NH∙∙∙F hydrogen bonding has been proposed to play a role in stabilizing conformers of certain 3

• delocalization is considered to be secondary [7]. However, stabilization via intramolecular hydrogen bonding does not seem to significantly impact the conformational stability of 3-fluoropiperidine. In this context, the cis-conformer, with the axial fluorine atom facing the N-hydrogen atom, is either equally or

• only slightly more stable than the other three conformers in both the gas phase and implicit water [4]. Hence, it appears that strong intramolecular interactions, and not only hydrogen bonding, govern the orientation of the fluorine atom in the F‒C‒C‒N fragment, favoring the cis-isomer of 3

Primary amine-catalyzed enantioselective 1,4-Michael addition reaction of pyrazolin-5-ones to α,β-unsaturated ketones

• Pooja Goyal,
• Akhil K. Dubey,
• Raghunath Chowdhury and
• Amey Wadawale

Beilstein J. Org. Chem. 2024, 20, 1518–1526, doi:10.3762/bjoc.20.136

• -covalent catalysis via bifunctional hydrogen-bonding organocatalysts. The C-4 nucleophilicity of pyrazolin-5-ones was also explored in enantioselective reactions with α,β-unsaturated carbonyl compounds through covalent catalysis with chiral amine-based catalysts; however, it has achieved limited success

• assembly) activates the pyrazol-5-one 2a through hydrogen bonding and forms the corresponding enol. Simultaneously, the enol form of the pyrazol-5-one attacks the Re-face of the α,β-unsaturated ketone 1b to provide the intermediate 5 (Scheme 5), which after hydrolysis leads to product ent-3ba'. In situ

Selectfluor and alcohol-mediated synthesis of bicyclic oxyfluorination compounds by Wagner–Meerwein rearrangement

• Ziya Dağalan,
• Muhammed Hanifi Çelikoğlu,
• Saffet Çelik,
• Ramazan Koçak and
• Bilal Nişancı

Beilstein J. Org. Chem. 2024, 20, 1462–1467, doi:10.3762/bjoc.20.129

• compounds by changing their metabolic stability, hydrogen bonding ability, lipophilicity, solubility, bioavailability, conformation and general structure [1][2][3][4]. About 20% of commercially available drugs contain fluorine, and this ratio is estimated to increase further [5][6]. Among organofluorines

Synthesis and physical properties of tunable aryl alkyl ionic liquids based on 1-aryl-4,5-dimethylimidazolium cations

• Stefan Fritsch and
• Thomas Strassner

Beilstein J. Org. Chem. 2024, 20, 1278–1285, doi:10.3762/bjoc.20.110

• blocked at the C2 position [33]. The use of a substituent at the C2 position was found to have a strong influence on the properties of these ionic liquids due to changes in the hydrogen-bonding network. Here, we investigate the properties of TAAILs based on the 1-aryl-4,5-dimethylimidazolium cation. It is

Competing electrophilic substitution and oxidative polymerization of arylamines with selenium dioxide

• Vishnu Selladurai and
• Selvakumar Karuthapandi

Beilstein J. Org. Chem. 2024, 20, 1221–1235, doi:10.3762/bjoc.20.105

• P21/c [49]. It adopts a transoid geometry around the oxamide C–C bond with nearly 180° torsion angle. This provides the molecule with a planar geometry. It shows intermolecular hydrogen bonding between the amide O and NH moieties. (Figure S35, Supporting Information File 1). Oxamide 9 crystallized in

• a monoclinic crystal system in the space group P21/c. The structure was similar to the structure of oxamide 3 (Figure 2). The hydrogen of the NH unit was concealed by the oxygen atoms of the C=O and OMe units. Consequently, it did not engage in intermolecular hydrogen bonding. Due to the planar

• . It crystallized in a triclinic crystal system in the space group P−1. It was structurally similar to the other oxamides 3 and 9. It showed an intramolecular hydrogen bonding between the NH and the carbonyl group of the methoxy ester. A layer-by-layer packing was observed in the crystal structure

Structure–property relationships in dicyanopyrazinoquinoxalines and their hydrogen-bonding-capable dihydropyrazinoquinoxalinedione derivatives

• Tural N. Akhmedov,
• Ajeet Kumar,
• Daken J. Starkenburg,
• Kyle J. Chesney,
• Khalil A. Abboud,
• Novruz G. Akhmedov,
• Jiangeng Xue and
• Ronald K. Castellano

Beilstein J. Org. Chem. 2024, 20, 1037–1052, doi:10.3762/bjoc.20.92

• 73019, United States 10.3762/bjoc.20.92 Abstract Presented here is the design, synthesis, and study of a variety of novel hydrogen-bonding-capable π-conjugated N-heteroacenes, 1,4-dihydropyrazino[2,3-b]quinoxaline-2,3-diones (DPQDs). The DPQDs were accessed from the corresponding weakly hydrogen

• -bonding dicyanopyrazinoquinoxaline (DCPQ) suspensions with excess potassium hydroxide, resulting in moderate to good yields. Both families of compounds were analyzed by UV–vis and NMR spectroscopy, where the consequences of hydrogen bonding capability could be assessed through the structure–property

• studies. Conversion of the DCPQs into hydrogen-bonding capable DPQDs results in modulation of frontier MO energies, higher molar extinction coefficients, enhanced crystallinity, and on-average higher thermal stability (where in some cases the 5% weight loss temperature is increased by up to 100 °C

Advancements in hydrochlorination of alkenes

• Daniel S. Müller

Beilstein J. Org. Chem. 2024, 20, 787–814, doi:10.3762/bjoc.20.72

• following mechanism (Scheme 30B): Initially, the terminal palladium species H, formed through the hydropalladation of terminal or internal alkenes (upon chain walking), coordinates to NCS via hydrogen bonding (I). Subsequent oxidation takes place to yield a Pd(IV) species (J), which then undergoes reductive

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

• substituted by two mesogenic cholesteryl groups (Figure 6) [28]. Due to strong hydrogen bonding between the pyridyl moiety and the N–H of the hydrazone, tweezers 5 predominantly exist in the closed E-form in a CD2Cl2 solution (E/Z-isomer ratio of 91:9). Upon protonation of the pyridyl group, a complete

• PtCl2 preorganizes the tweezers in a closed conformation with the two hydrogen-bonding-recognition sites in proximity. A significant increase in the binding affinity toward all anions and in particular for dihydrogen phosphate (log K = 3.5) was obtained. More recently, Álvarez and co-workers reported

• luminescence properties of the system could then be regulated by closing/opening but also by the addition of Cl− that could form hydrogen bonding with the amide function of the spacer between the switching and the functional units. The WLA has also been applied to obtain switchable molecular tweezers for

Ligand effects, solvent cooperation, and large kinetic solvent deuterium isotope effects in gold(I)-catalyzed intramolecular alkene hydroamination

• Ruichen Lan,
• Brock Yager,
• Yoonsun Jee,
• Cynthia S. Day and
• Amanda C. Jones

Beilstein J. Org. Chem. 2024, 20, 479–496, doi:10.3762/bjoc.20.43

• effect of MeOH co-solvent on the 1a → 3a transformation was due to its role as a hydrogen bonding donor (proton source), or due to its role as a hydrogen bonding acceptor (Lewis base) [44]. To this end, we examined the impact of different alcohols (varied acidity and polarity) and different non-protic

• effective in reactions that depend on hydrogen bonding activation [54], and the substrate effects observed here find some similarities in other Bronsted acid-catalyzed processes. In disulfonimide-catalyzed asymmetric intramolecular hydroamination of alkenyl thioureas, sulfonamides are unreactive compared to

• thioureas and the reaction is favored at lower concentrations, an impact proposed to be due to hydrogen bonding driven self-association of the substrate [55]. In other Bronsted acid-catalyzed processes, thioureas and ureas are both effective substrates, with higher reactivity associated with thioureas

Green and sustainable approaches for the Friedel–Crafts reaction between aldehydes and indoles

• Periklis X. Kolagkis,
• Eirini M. Galathri and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2024, 20, 379–426, doi:10.3762/bjoc.20.36

• interesting alternative to hydrogen bonding, which constitute an indispensable type of non-covalent interaction utilized in several catalytic approaches [81][82][83][84][85][86][87][88]. In 2008, Bolm introduced the use of perfluoroiodoalkanes as XB catalysts and the field gained widespread attention as an

• to the employment of GO–CuBr without overshadowing its applications [113]. Shirini et al. utilized the polymer poly(4-vinylpyridine) (P4VPy) for the immobilization of nanoparticles in lieu of silica, due to the strong affinity of the pyridyl group towards metals and its ability to undergo hydrogen

• bonding with polar species [114]. The nanoparticle of choice was CuO, which had already displayed several varied catalytic applications, so the P4VPy–CuO nanoparticles were synthesized through an ultrasound irradiation protocol and tested in the reaction between p-chlorobenzaldehyde and indole. An amount

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• undergo addition to the heterocyclic radical acceptor 19 through a ternary transition state 20 involving hydrogen bonding interactions with the chiral phosphate co-catalyst. Notably, a follow-up report revealed that the radical addition is reversible, and that the selectivity determining step involves the

• can occur through hydrogen bonding. In the proposed mechanism (Scheme 6B), hydrogen bonded complex 24 undergoes single electron reduction via oxidative quenching of the excited state *IrIII, resulting in the formation of radical anion 25 (presumably H-bonded to H2O) and the corresponding IrIV complex

• oxyalkylation product 28. Li and co-workers described the activation of NHPI esters towards SET using a Lewis acid catalyst, allowing for the functionalization of styrene radical acceptors with nucleophiles that do not necessarily engage in hydrogen-bonding interactions, such as electron-rich (hetero)arenes [47

Spatial arrangements of cyclodextrin host–guest complexes in solution studied by ¹³C NMR and molecular modelling

• Konstantin Lebedinskiy,
• Ivan Barvík,
• Zdeněk Tošner,
• Ivana Císařová,
• Jindřich Jindřich and
• Radim Hrdina

Beilstein J. Org. Chem. 2024, 20, 331–335, doi:10.3762/bjoc.20.33

• dispersion forces and hydrogen bonding between the cyclodextrin (CD) unit and the guest molecule. Determination of the ee of chiral guests was achieved by observing the splitting of 1H NMR signals of the achiral host upon formation of diastereomeric inclusion complexes [18][19]. Shifting the H-3 and H-5

Elucidating the glycan-binding specificity and structure of Cucumis melo agglutinin, a new R-type lectin

• Jon Lundstrøm,
• Emilie Gillon,
• Valérie Chazalet,
• Nicole Kerekes,
• Antonio Di Maio,
• Ten Feizi,
• Yan Liu,
• Annabelle Varrot and
• Daniel Bojar

Beilstein J. Org. Chem. 2024, 20, 306–320, doi:10.3762/bjoc.20.31

• would lead to steric clashes and loss of strong hydrogen bonding. In the LacNAc-complexed structure (PDB ID 8R8A) [29], the GlcNAc residue did not seem to engage in extensive interactions, with only a hydrogen bond between the N-acetyl moiety and the main chain oxygen of Gly24 and hydrophobic

• . While no direct interactions with the protein backbone were observed, we found one water molecule to mediate hydrogen bonding between the oxygen of the N-acetyl group and the Asn43 side chain oxygen (Figure 4d). Both GalNAc anomers could be observed, showing interactions through water molecule

Additive-controlled chemoselective inter-/intramolecular hydroamination via electrochemical PCET process

• Kazuhiro Okamoto,
• Naoki Shida and
• Mahito Atobe

Beilstein J. Org. Chem. 2024, 20, 264–271, doi:10.3762/bjoc.20.27

• phenoxide in PhOH, the PhOH molecule is included in the hydrogen bond network along with the tetrabutylammonium cation (Bu4N+) to form a large aggregate. The hydrogen bonding between the amide and phosphate base in the small aggregates was stronger than in the large aggregates, which significantly enhanced

Substitution reactions in the acenaphthene analog of quino[7,8-h]quinoline and an unusual synthesis of the corresponding acenaphthylenes by tele-elimination

• Ekaterina V. Kolupaeva,
• Narek A. Dzhangiryan,
• Alexander F. Pozharskii,
• Oleg P. Demidov and
• Valery A. Ozeryanskii

Beilstein J. Org. Chem. 2024, 20, 243–253, doi:10.3762/bjoc.20.24

• reaction with neutral or anionic bases. Keywords: dipyrido[3,2-e:2′,3′-h]acenaphthene (acenaphthylene); hydrogen bonding; π-stacking; substitution reactions; tele-elimination; Introduction Quinoline derivatives, classical nitrogen-containing heterocycles, are widely distributed in nature in various forms

• , dipyridoacenaphthene chloride dihydrate, its 2:1 complex with 4,6-dichlororesorcinol, and neutral dipyridoacenaphthene as a self-associate were obtained and structurally characterized for the first time. The dominant feature of all crystal structures is the intramolecular NHN hydrogen bonding in combination with π

Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• melting point of indigo is bifurcated intra- and intermolecular hydrogen bonding [11], and face-to-face π–π stacking of parallel aromatic rings (Figure 2) [12]. Single crystal X-ray diffraction analysis showed that the indigo molecule is almost planar and exists in the E-conformation. The central C=C bond

• the Z-isomers in comparison with the E-forms [62]. In 2018, Nagasawa and co-workers provided a detailed investigation of the influence of solvent polarity and intermolecular hydrogen bonding on the photoisomerization of N,N'-diacetylindigo (9a) by transient absorption spectroscopy [63]. In principle

• , it was already known that the intermolecular hydrogen bonding with solvent molecules may hinder the photoisomerization of indigo derivatives [46]. Nagasawa and co-workers found that the photoisomerization of 9a was inhibited by polar DMF due to formation of weak hydrogen bonds with formyl groups

Perspectives on push–pull chromophores derived from click-type [2 + 2] cycloaddition–retroelectrocyclization reactions of electron-rich alkynes and electron-deficient alkenes

• Michio Yamada

Beilstein J. Org. Chem. 2024, 20, 125–154, doi:10.3762/bjoc.20.13

• substructures. Consequently, the macrocycle was tethered to the peptide segment through amide–amide hydrogen bonding, and 44 was obtained with 30% yield. The generation of 44 was accompanied by the formation of the corresponding free thread with 62% yield, resulting from the reaction between the thread

• arising from hydrogen bonding and π–π stacking interactions. In contrast, when 75 is incorporated into a nanocomposite with polystyrene serving as the matrix, luminescent properties are observed [141]. Photoinduced intramolecular energy and electron transfer Exploiting the electron-accepting property of