Aromatic C–H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel–Crafts reaction: a recent update

• Anup Biswas

Beilstein J. Org. Chem. 2023, 19, 956–981, doi:10.3762/bjoc.19.72

• stereoselectivity is also explained. Keywords: asymmetric; aza-Friedel–Crafts reaction; H-bonding; organocatalysis; stereoselectivity; Introduction The ease of a chemical transformation depends on the thermodynamic instability of a chemical bond owing to its fast cleavage under mild reaction conditions. A C–H

• the reaction partners in a highly ordered three dimensional transition state through noncovalent interactions (like H-bonding, π–π interactions) thus promoting the stereoselective reaction. Examples of covalent bonding organocatalysts are amines [6][7], N-heterocyclic carbenes [8][9], phosphines [10

• –Crafts reaction has also been explored under the influence of organocatalysis. However, here organocatalysts act as Brønsted acids which form noncovalent interactions (H-bonding) with the imine nitrogen to enhance the electrophilicity of the imine component. In addition, by selecting suitable imine

Functionalization of imidazole N-oxide: a recent discovery in organic transformations

• Koustav Singha,
• Imran Habib and
• Mossaraf Hossain

Beilstein J. Org. Chem. 2022, 18, 1575–1588, doi:10.3762/bjoc.18.168

• , the authors revealed the product 4a as E-isomer due to the strong intramolecular H-bonding. It was also observed that the labile acetal group in the product 4g remained unaffected during the reaction process under the standard conditions. Imidazole N-oxides reacted with ethyl cyanoacetate to produce

Heteroleptic metallosupramolecular aggregates/complexation for supramolecular catalysis

• Prodip Howlader and
• Michael Schmittel

Beilstein J. Org. Chem. 2022, 18, 597–630, doi:10.3762/bjoc.18.62

• , which entailed the quantitative formation of the edge-directed molecular prism 15 (Figure 3). The adequate length of the ditopic clip 13 constrained the urea triangle from intersupramolecular H-bonding. Thus, the urea moieties in this newly assembled 3D architecture were freely available for

• interactions with appropriate guest molecules through H-bonding. Different organic molecules, such as nitroolefins, capable of forming H-bonding with the urea moieties inside the cavity were investigated in water for their ability to encapsulate in the cavity under heterogeneous conditions. Successful binding

• . For this purpose, they have chosen the ditopic bisurea “strut” 12 (Figure 3), which generated a 2D discrete molecular triangle 14 in the presence of an equimolar amount of the cis-(tmen)Pd(NO3)2 acceptor 5 [59]. In order to prevent the urea moieties on the triangle to get engaged in intermolecular H

A resorcin[4]arene hexameric capsule as a supramolecular catalyst in elimination and isomerization reactions

• Tommaso Lorenzetto,
• Fabrizio Fabris and
• Alessandro Scarso

Beilstein J. Org. Chem. 2022, 18, 337–349, doi:10.3762/bjoc.18.38

• series of control experiments supported in all cases the evidence that the reaction is not just promoted by the acidity of 16 or its H-bonding properties, but that a combination of weak Brønsted acidity together with the presence of an accessible electron-rich cavity that favors the stabilization of the

• recorded after 64 h at room temperature, while A and B were recorder right after sample preparation. Resorcin[4]arene 1 forming the corresponding hexameric capsule 16 and the species used for control experiments like 4-n-hexylresorcinol (2) to mimic the H-bonding properties of the capsule

Organocatalytic asymmetric nitroso aldol reaction of α-substituted malonamates

• Ekta Gupta,
• Narendra Kumar Vaishanv,
• Sandeep Kumar,
• Raja Krishnan Purshottam,
• Ruchir Kant and
• Kishor Mohanan

Beilstein J. Org. Chem. 2022, 18, 217–224, doi:10.3762/bjoc.18.25

• on the screening of various bifunctional H-bonding catalysts, and in this regard, the reaction catalyzed by quinine-derived thiourea catalyst 3b furnished the product 4a in 55% yield and 71% ee (Table 1, entry 5). The other enantiomer was obtained when the reaction was carried out using the

Green synthesis of C5–C6-unsubstituted 1,4-DHP scaffolds using an efficient Ni–chitosan nanocatalyst under ultrasonic conditions

• Soumyadip Basu,
• Sauvik Chatterjee,
• Suman Ray,
• Suvendu Maity,
• Prasanta Ghosh,
• Asim Bhaumik and
• Chhanda Mukhopadhyay

Beilstein J. Org. Chem. 2022, 18, 133–142, doi:10.3762/bjoc.18.14

• H-bonding. The presence of diffraction peaks at 2Θ 9.2 and 19.7 (in degree) indicated the presence of a chitosan framework [28], whereas the other minor diffraction peaks were observed due to the presence of Ni(II). From the SEM and TEM images of the catalyst, we confirmed the morphological features

N-Sulfinylpyrrolidine-containing ureas and thioureas as bifunctional organocatalysts

• Viera Poláčková,
• Dominika Krištofíková,
• Boglárka Némethová,
• Renata Górová,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2021, 17, 2629–2641, doi:10.3762/bjoc.17.176

• , including enantioselective H-bonding-catalyzed additions to aliphatic N-Boc-imines with high stereoselectivity [22]. A broad range of β-aminonitroolefins were reduced to chiral β-aminonitroalkanes in high yields and excellent enantioselectivities using trichlorosilane as a reducing agent and an N

Halides as versatile anions in asymmetric anion-binding organocatalysis

• Lukas Schifferer,
• Martin Stinglhamer,
• Kirandeep Kaur and
• Olga García Macheño

Beilstein J. Org. Chem. 2021, 17, 2270–2286, doi:10.3762/bjoc.17.145

• reported a family of chiral helical tetratriazoles 82 as a new class of anion-binding catalysts, which can be considered as supramolecular anion-binding catalysts (Scheme 18) [22]. Not only is the increased H-bonding network in multidentate 82 beneficial for giving a firm control over both regio- and

• examples, and the advance of anion-binding-catalyzed strategies involving more complex H-bonding networks clearly highlight that it is indeed possible to mimic enzyme-like structures with small-molecule catalysts for asymmetric synthesis. Conclusion In the past two decades, tremendous advances in the field

• , in which differentiation between classical H-bonding to neutral substrates and the binding to anionic species was delineated, anion-binding interactions became more prominent and started being considered in the design of new syntheses and catalytic approaches. In this context, the emphasis was to

Enantioenriched α-substituted glutamates/pyroglutamates via enantioselective cyclopropenimine-catalyzed Michael addition of amino ester imines

• Zara M. Seibel,
• Jeffrey S. Bandar and
• Tristan H. Lambert

Beilstein J. Org. Chem. 2021, 17, 2077–2084, doi:10.3762/bjoc.17.134

• reported [45], for which a detailed transition state model was developed. In that study, it was determined that the reaction proceeds via several competing low-energy transition states involving both O–H and N–H enolate binding modes, E and Z enolate isomers, and a range of H-bonding and other noncovalent

A study on selective transformation of norbornadiene into fluorinated cyclopentane-fused isoxazolines

• Zsanett Benke,
• Attila M. Remete and
• Loránd Kiss

Beilstein J. Org. Chem. 2021, 17, 2051–2066, doi:10.3762/bjoc.17.132

• observed selectivities in metathesis reactions, H-bonding interactions between chloride ligands as H-bond acceptors and OH or NH functions in the metathesis intermediate appear to be determining [35][36]. Selectivity derived from chelation is considered to be an another important contributor. Through the

Icilio Guareschi and his amazing “1897 reaction”

• Gian Cesare Tron,
• Alberto Minassi,
• Giovanni Sorba,
• Mara Fausone and
• Giovanni Appendino

Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93

• ⋅mol−1) and favored over abstraction by a hydroperoxy radical, which would be only exothermic by 2 kcal⋅mol−1. The exothermicity of the hydrogen abstraction reaction is reduced with stabilized radicals, which have weaker C–H bonding. In this case, trapping by dissolved oxygen competes, generating a

Synthetic accesses to biguanide compounds

• Oleksandr Grytsai,
• Cyril Ronco and
• Rachid Benhida

Beilstein J. Org. Chem. 2021, 17, 1001–1040, doi:10.3762/bjoc.17.82

• intramolecular H-bond character. The second protonation rather takes place on the N3 nitrogen atom, causing planar character disruption and preventing H-bonding (Figure 2) [1]. Biguanide derivatives often display low melting points (mp = 136 °C for simple biguanide). However, above 130 °C, a concomitant thermal

Beyond ribose and phosphate: Selected nucleic acid modifications for structure–function investigations and therapeutic applications

• Christopher Liczner,
• Kieran Duke,
• Gabrielle Juneau,
• Martin Egli and
• Christopher J. Wilds

Beilstein J. Org. Chem. 2021, 17, 908–931, doi:10.3762/bjoc.17.76

DNA with zwitterionic and negatively charged phosphate modifications: Formation of DNA triplexes, duplexes and cell uptake studies

• Yongdong Su,
• Maitsetseg Bayarjargal,
• Tracy K. Hale and
• Vyacheslav V. Filichev

Beilstein J. Org. Chem. 2021, 17, 749–761, doi:10.3762/bjoc.17.65

• cell-based applications. Illustration of H-bonding in a DNA duplex and a parallel triplex. A) Depiction of Watson–Crick base-paring (left: T-A and right: C-G); B) parallel triple helices: pyrimidine-rich third strand interactions are stabilised by Hoogsteen hydrogen bonds (the duplex is in black, TFO

Selected peptide-based fluorescent probes for biological applications

• Debabrata Maity

Beilstein J. Org. Chem. 2020, 16, 2971–2982, doi:10.3762/bjoc.16.247

• -aminobutyric acid associate with membrane-bound protein receptors and trigger changes in receptor shape and activity with subsequent signaling across the membrane. Noncovalent H-bonding and van der Waals interactions are the basis for the selective molecular recognition between a G-coupled protein receptor and

Using multiple self-sorting for switching functions in discrete multicomponent systems

• Amit Ghosh and
• Michael Schmittel

Beilstein J. Org. Chem. 2020, 16, 2831–2853, doi:10.3762/bjoc.16.233

• undemanding building blocks. The plethora of self-sorting systems depends on either the geometric fit of their global shapes and/or matching of their local interactions. Various noncovalent interactions, such as H‐bonding [8][9], metal–ligand coordination [10][11][12][13], electrostatic interactions [14], π

• . Some selected self-sorting outcomes and their qualitative and quantitative assessment. Illustration of an integrative vs a non-integrative self-sorting. The pH-driven four-component 2-fold completive self-sorting based on host–guest chemistry. (a) The monomers 5 and 6 and their H-bonding array. (b) The

Selective recognition of ATP by multivalent nano-assemblies of bisimidazolium amphiphiles through “turn-on” fluorescence response

• Rakesh Biswas,
• Surya Ghosh,
• Shubhra Kanti Bhaumik and
• Supratim Banerjee

Beilstein J. Org. Chem. 2020, 16, 2728–2738, doi:10.3762/bjoc.16.223

• . One of the challenges in the bio-anion detection is that the sensory probes have to be effective under physiological conditions. The highly polar nature of the aqueous media considerably weakens supramolecular interactions such as H-bonding and electrostatic interactions and as a result, it is in

NMR Spectroscopy of supramolecular chemistry on protein surfaces

• Peter Bayer,
• Anja Matena and
• Christine Beuck

Beilstein J. Org. Chem. 2020, 16, 2505–2522, doi:10.3762/bjoc.16.203

pH- and concentration-dependent supramolecular self-assembly of a naturally occurring octapeptide

• Goutam Ghosh and
• Gustavo Fernández

Beilstein J. Org. Chem. 2020, 16, 2017–2025, doi:10.3762/bjoc.16.168

• two peptides increases in twisted β-sheets, the H-bonding distances increase, weakening the intermolecular forces. At basic pH values, the carboxyl group of Glu is present as a negatively charged carboxylate species, thereby inducing weak electrostatic repulsions between Glu− residues, which may be

A dynamic combinatorial library for biomimetic recognition of dipeptides in water

• Florian Klepel and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2020, 16, 1588–1595, doi:10.3762/bjoc.16.131

• (Figure S10, Supporting Information File 1). This behavior does not contradict the ITC measurements and can be attributed to the kinetic isotope effect. Although, D-bonding is generally stronger than H-bonding, its contribution to the peptide–peptide binding can be weakened by even stronger competitive

Five-component, one-pot synthesis of an electroactive rotaxane comprising a bisferrocene macrocycle

• Natalie Lagesse,
• Luca Pisciottani,
• Maxime Douarre,
• Pascale Godard,
• Brice Kauffmann,
• Vicente Martí-Centelles and
• Nathan D. McClenaghan

Beilstein J. Org. Chem. 2020, 16, 1564–1571, doi:10.3762/bjoc.16.128

• prove a valuable component for the construction of novel redox-active supramolecular systems, such as rotaxanes with strongly binding H-bonding templating sites, or indeed juxtaposed into existing functional architectures and benchmark variants. Results and Discussion Synthesis Our first approach to the

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• engage with the peptide backbone via an H-bonding interaction, and in order to achieve a high enantioselectivity, the amide functionalization of the peptide at the 4-proline position is essential. Amide-substituted vinylcyclopropanes have a relatively good H-bond-donating ability, so they are more

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

• large number of alcohols (5a–e) in the presence of base (KOH 1 mol %). An interesting strategy aiming to explore the possibility of interfacing the redox-activity with H-bonding ability inside the ligand coordination sphere has been disclosed by Swart and Garcia-Bosch [16], and relies on the design and

• study of a new copper(II) complex. A family of o-phenylenediamido ligands was synthesized through the introduction of ureanyl groups, using a synthetic approach developed by Borovik [17][18] for the stabilization of metal–oxo and metal–hydroxo complexes via intramolecular H-bonding interactions. The

• resulting copper complexes were synthesized and single crystal X-ray diffraction analysis evidenced the existence of H-bonding inside the coordination sphere of 6 (Scheme 3). The authors reported that the influence of the geometry of the complex on the H-bonding interactions as well as the nature of this

Recent advances in photocatalyzed reactions using well-defined copper(I) complexes

• Mingbing Zhong,
• Xavier Pannecoucke,
• Philippe Jubault and
• Thomas Poisson

Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42

• structure and to carry out an SET when excited by light. This approach represents the first report describing the design of a Cu-based photocatalyst able to carry out an SET and an activation of the substrate, in this case through H-bonding. This close proximity increased the yield of the transformation and

• reaction was excellent as bromides, phenols, thioethers, esters, boronic esters, and heterocycles, including pyridine and quinolines, were well tolerated. The authors carried out mechanistic studies and demonstrated the H-bonding ability of their catalyst by NMR studies. The following mechanism was

Synthesis and characterization of bis(4-amino-2-bromo-6-methoxy)azobenzene derivatives

• David Martínez-López,
• Amirhossein Babalhavaeji,
• Diego Sampedro and
• G. Andrew Woolley

Beilstein J. Org. Chem. 2019, 15, 3000–3008, doi:10.3762/bjoc.15.296

• elevated pKa of 1 has been attributed to resonance stabilization of the azonium cation together with intramolecular H-bonding between the azonium proton and methoxy groups in ortho-position to the azo double bond [10]. Since the azonium ion 1 forms under physiological conditions, i.e., at neutral pH value