Isolation and structure determination of a tetrameric sulfonyl dilithio methandiide in solution based on crystal structure analysis and ⁶Li/¹³C NMR spectroscopic data

• Jürgen Vollhardt,
• Hans Jörg Lindner and
• Hans-Joachim Gais

Beilstein J. Org. Chem. 2020, 16, 2057–2063, doi:10.3762/bjoc.16.172

• couplings shows, however, that the carbon lithium bonds in 2a-I have a covalent contribution as generally observed for organolithiums [55]. Three mechanisms most likely contribute to the stabilization of the negative charge of the carbon atoms of tetramer (2a)4·(THF)6 and hexamer (2a)6·Li2O·(THF)6

• , electrostatic interaction with and charge polarization by the positively charged sulfur atom [56] and silicon atom [57], and negative nC–σ*SPh hyperconjugation [56][58]. The anions of (2a)4·(THF)6 and (2a)6·Li2O·(THF)6 adopt conformations around the carbon sulfur bond, which would allow for stabilization by

Synergy between supported ionic liquid-like phases and immobilized palladium N-heterocyclic carbene–phosphine complexes for the Negishi reaction under flow conditions

• Edgar Peris,
• Raúl Porcar,
• María Macia,
• Jesús Alcázar,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2020, 16, 1924–1935, doi:10.3762/bjoc.16.159

• enhanced precatalyst preparation, stabilization and initiation, PEPPSI) [23][24]. In addition to pyridine ligands, other compounds with coordinating atoms such as C, N or P have been reported to tune the catalytic activity of the NHC–Pd complexes [25][26][27][28]. Thus, a ligand containing P as the

• catalyst but also will generate and release a series of Pd species accounting for the leaching. The second component, the SILLP, can act as scavenger of those species leached to the solution not only eliminating them from the solution but also contributing to their stabilization avoiding the formation of

• , Ananikov and co-workers reported that for Pd–NHC systems the reactivity of the systems is mainly determined by the cleavage of the metal−NHC bond, while the catalyst performance is strongly affected by the stabilization of in situ-formed metal clusters [15][30][40]. In the mechanism suggested by these

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

• Vladimir Kubyshkin

Beilstein J. Org. Chem. 2020, 16, 1837–1852, doi:10.3762/bjoc.16.151

• substitution of proline with analogues can result in the conformational stabilization and polarity effects competing with each other [58]. Finally, it has been shown that fluoroprolines can alter donor–acceptor interactions of the proline ring with a tryptophan residue [59]. All these findings indicate that

• experimental 2-CH multiplicity with the one predicted for the pure conformers (Figure 4). As can be seen from the data, both fluoroprolines exhibited stabilization of certain side-chain conformers: the cis-isomer 1 stabilized the C4-endo envelope, whereas the trans-isomer 2 stabilized the C4-exo (Figure 5

• origin of the effect is orbital (the gauche-effect) rather than through space dipolar interaction (assuming that an interaction of dipoles would be attenuated in polar solvents, which was not observed). A stabilization of certain side-chain conformers was also observed in the trifluoromethylated

One-pot synthesis of oxazolidinones and five-membered cyclic carbonates from epoxides and chlorosulfonyl isocyanate: theoretical evidence for an asynchronous concerted pathway

• Esra Demir,
• Ozlem Sari,
• Yasin Çetinkaya,
• Ufuk Atmaca,
• Safiye Sağ Erdem and
• Murat Çelik

Beilstein J. Org. Chem. 2020, 16, 1805–1819, doi:10.3762/bjoc.16.148

• . Noteworthy, the C2–N4 bond length does not change much along the IRC for the formation of 10; however, it is shortened more rapidly to give 11. The presence of partial double bond between C2–C(Ph) (benzylic position) allows electron delocalization around the reacting center, which results in stabilization of

• the transition state and so lowering the activation energy barrier (Figure 3a). On the other hand, stabilization of the benzylic cation is not possible along the IRC path for TS1′ (Figure 3b), since the bond distance C2–C(Ph) is found as around 1.50 Å showing a single bond character. This can be the

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

• –acceptor distances: 2.2–2.5 Å “strong, mostly covalent”, 2.5–3.2 Å “moderate, mostly electrostatic”, and 3.2–4.0 Å “weak, electrostatic” [23]. The corresponding stabilization energies were estimated to be in the ranges 40–14 kcal/mol, 15–4 kcal/mol, and < 4 kcal/mol, respectively. The macrocycle

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• -substituted cation 19 favors the radical cyclization path because the stabilization by an α-substituent makes its cation center more stable and less reactive. In contrast, the non-α-substituted cation 19 prefers the cationic cyclization. However, the two cyclization processes form the intermediates 20 and 21

Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole

• Carlos H. Escalante,
• Eder I. Martínez-Mora,
• Carlos Espinoza-Hicks,
• Alejandro A. Camacho-Dávila,
• Fernando R. Ramos-Morales,
• Francisco Delgado and
• Joaquín Tamariz

Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113

• displays a Cethynyl–H···π interaction (2.530 Å) between the acetylene proton of 8j and the N-phenyl ring of the N-phenylmaleimide (7c) (Table 7, and Figure 4d and Figure 5c). Such an interaction may explain the greater stabilization of the endo approach to give 9p as the major isomer. Due to the scarce X

Activated carbon as catalyst support: precursors, preparation, modification and characterization

• Melanie Iwanow,
• Tobias Gärtner,
• Volker Sieber and
• Burkhard König

Beilstein J. Org. Chem. 2020, 16, 1188–1202, doi:10.3762/bjoc.16.104

• /O elemental analysis, EDX, XPS, XRD and TGA. Keywords: activated carbon; catalysis; characterization techniques; metal supported on carbon catalysts; preparation methods; Introduction Support materials for metal catalysts allow the dispersion and stabilization of small metal particles on a surface

Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis

• Stephanie G. E. Amos,
• Marion Garreau,
• Luca Buzzetti and
• Jerome Waser

Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103

• carboxylates. Aminyl and aminium radical generation The prevalent strategy for accessing aminium radicals is SET oxidations. The efficiency of this approach is closely related to the stabilization of the generated radical on the substrate (delocalization, electronic effects) or through a strain release ring

Fluorinated phenylalanines: synthesis and pharmaceutical applications

• Laila F. Awad and
• Mohammed Salah Ayoup

Beilstein J. Org. Chem. 2020, 16, 1022–1050, doi:10.3762/bjoc.16.91

• improve protein stability, natural hydrocarbon amino acids were replaced with Pff 77a. The effect of enhanced protein stability upon this replacement is referred as to ‘fluoro-stabilization effect’ [56]. 1.7. Knoevenagel condensation of methyl isocyanoacetate Three isomers of fluorinated phenylalanines

Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties

• Liliia Moshniaha,
• Marika Żyła-Karwowska,
• Joanna Cybińska,
• Piotr J. Chmielewski,
• Ludovic Favereau and
• Marcin Stępień

Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81

• HOMOs by about 0.5 eV while relative stabilization of the LUMO approaches 1 eV with respect to cNMI3H and cNMI2H. This comparably stronger LUMO stabilization in the NMI lactam systems results in a considerable decrease of their electrochemical gap (ΔE, by ca. 0.5–0.7 V), relative to the α-free analogues

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

• presence of base (Cs2CO3). The results suggested that 2 is more efficient than 1 and this reactivity difference could be attributed to an increased stabilization of the involved reactive catalytic intermediates by the electron-donating acetate ions present in complex 2. The same team later reported on

• 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

Synthesis of C₇₀-fragment buckybowls bearing alkoxy substituents

• Yumi Yakiyama,
• Shota Hishikawa and
• Hidehiro Sakurai

Beilstein J. Org. Chem. 2020, 16, 681–690, doi:10.3762/bjoc.16.66

• same stacking direction were arranged along the a axis, while an alternative stacking direction was observed along the c axis. Although relatively low diffraction data quality prohibited the detailed discussion about the interaction distances, the stabilization of the 1-dimensional stacking column of

Regioselectively α- and β-alkynylated BODIPY dyes via gold(I)-catalyzed direct C–H functionalization and their photophysical properties

• Takahide Shimada,
• Shigeki Mori,
• Masatoshi Ishida and
• Hiroyuki Furuta

Beilstein J. Org. Chem. 2020, 16, 587–595, doi:10.3762/bjoc.16.53

• nodal plane near the 1,7-positions in the HOMO and smaller MO coefficients at the 2,6-positions than those at the 3,5-positions. Rather, a stabilization of the LUMO energies is found in 5a and 6a even though the MO hybridization of the BODIPY core with π-orbitals of ethynyl moieties is less affected

Architecture and synthesis of P,N-heterocyclic phosphine ligands

• Wisdom A. Munzeiwa,
• Bernard Omondi and
• Vincent O. Nyamori

Beilstein J. Org. Chem. 2020, 16, 362–383, doi:10.3762/bjoc.16.35

• attributed this to a stabilization of the NH proton by hydrogen bonds to the triazole nitrogen and methoxy oxygen atoms. The initial step in the synthesis of 120 is the enantioselective synthesis of the propargylamine 118 through the reaction of propargyl acetate 117 with the corresponding amine. This

Synthesis, liquid crystalline behaviour and structure–property relationships of 1,3-bis(5-substituted-1,3,4-oxadiazol-2-yl)benzenes

• Afef Mabrouki,
• Malek Fouzai,
• Armand Soldera,
• Abdelkader Kriaa and
• Ahmed Hedhli

Beilstein J. Org. Chem. 2020, 16, 149–158, doi:10.3762/bjoc.16.17

• intermediate phase between 118.0 °C and 138.4 °C in heating and between 96.5 °C and 121.1 °C in cooling, indicating a remarkable stabilization in a temperature range of 20 °C. Polarized optical microscopy (POM) In order to achieve a further illustration of the liquid crystal behavior, POM observations were

[1,3]/[1,4]-Sulfur atom migration in β-hydroxyalkylphosphine sulfides

• Katarzyna Włodarczyk,
• Piotr Borowski and
• Marek Stankevič

Beilstein J. Org. Chem. 2020, 16, 88–105, doi:10.3762/bjoc.16.11

• that this transformation was reversible, and therefore the dication IV may have entered an alternative pathway, which involved the rotation of the molecule around the Cα–Cβ bond (activation barrier: +5.4 kcal/mol, stabilization: −3.4 kcal/mol), which was feasible under the reaction conditions. The

• , leading to intermediate I, and the overall transformation proceeded with remarkable stabilization. In the next step, dissociation of the C−O bond occurred through transition state II, finally leading to alkene III. The activation energy for the C−O bond cleavage in 20, a tertiary alcohol, was similar to

• different pathways. A complex of 19 with AlCl3 underwent simultaneous C–O bond cleavage and α-hydrogen (but not γ-hydrogen) atom abstraction, which led to 35, with activation barrier of +24.8 kcal/mol and a stabilization energy of −16.1 kcal/mol. Yet, at the moment, this preference remains to be further

Photocontrolled DNA minor groove interactions of imidazole/pyrrole polyamides

• Sabrina Müller,
• Jannik Paulus,
• Jochen Mattay,
• Heiko Ihmels,
• Veronica I. Dodero and
• Norbert Sewald

Beilstein J. Org. Chem. 2020, 16, 60–70, doi:10.3762/bjoc.16.8

• derivatives was proven by CD titration experiments. The resulting induced circular dichroism (ICD) bands of the bound ligands, together with the photometric determination of the dsDNA melting temperature, revealed a significant stabilization of the DNA upon association with the ligand. The (Z)-azobenzene

• can be observed by CD, too. The melting temperature (Tm) corresponds to the point of inflection where 50% of the DNA molecules are single-stranded. Tm depends on the number and strength of intramolecular interactions between the single strands, providing information on stabilization or destabilization

• melting temperature Tm of the dsDNA increased in the presence of the three polyamides Z-P1, Z-P2, and Z-P3, although it is also possible that during heating, thermally induced isomerization to the E-isomer occurred (Table 1). The highest stabilization value of the corresponding target sequences was

Understanding the role of active site residues in CotB2 catalysis using a cluster model

• Keren Raz,
• Ronja Driller,
• Thomas Brück,
• Bernhard Loll and
• Dan T. Major

Beilstein J. Org. Chem. 2020, 16, 50–59, doi:10.3762/bjoc.16.7

• /mol (Figure 1). Another possible reason for the stabilization was that C7 had a greater proximity to the pyrophosphate group than C15 (6.71 Å vs 7.54 Å, Table 1 and Figure 2). The energy difference between B and C was 15.7 kcal/mol in the active site model, compared to 8.7 kcal/mol in the gas phase

• . Here, the energy gain was likely due to the fact that the carbocation in intermediate C was located 4.21 Å away from the pyrophosphate group, which stabilized it (Table 1 and Figure 2). Moreover, π–cation interactions with F107 contributed to the stabilization as well. The activation energy for the

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

Why do thioureas and squaramides slow down the Ireland–Claisen rearrangement?

• Dominika Krištofíková,
• Juraj Filo,
• Mária Mečiarová and
• Radovan Šebesta

Beilstein J. Org. Chem. 2019, 15, 2948–2957, doi:10.3762/bjoc.15.290

• rearrangements of O-allyl β-ketoesters [35][36][37]. Hiersemann and Strassner studied the Claisen rearrangement with H-bond-donating organocatalysts by computational methods and concluded that thioureas are not efficient in transition-state stabilization [38]. Regarding the usefulness of the Ireland–Claisen

• for this difference, however, remains unclear. The explanation may be connected to a more compact transition state of sigmatropic rearrangements than their starting materials, which is thus less amenable to additional stabilization via hydrogen-bonding catalysts. To get further insight, we have

Bacterial terpene biosynthesis: challenges and opportunities for pathway engineering

• Eric J. N. Helfrich,
• Geng-Min Lin,
• Christopher A. Voigt and
• Jon Clardy

Beilstein J. Org. Chem. 2019, 15, 2889–2906, doi:10.3762/bjoc.15.283

• -en-7-ol (23, Figure 7a) synthase, for which the active-site residues responsible for cationic intermediate stabilization were identified through analysis of the crystal structure [122] and structural modeling [123]. Mutations of the identified residues were shown to alter product profiles and yielded

Influence of the cis/trans configuration on the supramolecular aggregation of aryltriazoles

• Sara Tejera,
• Giada Caniglia,
• Rosa L. Dorta,
• Andrea Favero,
• Javier González-Platas and
• Jesús T. Vázquez

Beilstein J. Org. Chem. 2019, 15, 2881–2888, doi:10.3762/bjoc.15.282

• stabilization of the supramolecular aggregation of bis(4-bromophenyl)triazoles. The trans or cis spatial disposition of the triazole rings is highly important for gelation, with the cis configuration having higher propensity. Keywords: circular dichroism; cis/trans configuration; gels; triazole; X-ray

• and 8e point at the fact that the presence of either the phenyl groups or the bromine atoms are not strictly necessary for gelation, although both might contribute to an overall stabilization of the supramolecular aggregation. Optical micrographs of the xerogels formed from compounds 7f, 8f, 10, 12

A chiral self-sorting photoresponsive coordination cage based on overcrowded alkenes

• Constantin Stuckhardt,
• Diederik Roke,
• Wojciech Danowski,
• Edwin Otten,
• Sander J. Wezenberg and
• Ben L. Feringa

Beilstein J. Org. Chem. 2019, 15, 2767–2773, doi:10.3762/bjoc.15.268

• structure determination [13][14] and stabilization of reactive species [15][16][17]. The use of reversible metal–ligand coordination bonds gives rise to systems that allow for adaption to external stimuli such as pH, anions, electric potential, concentration and light [4][8][18][19][20][21]. Using light to

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• pyrazole moiety, causing a tilting of the heteroring away from orthogonality with respect to the benzene plane (from θ = 90° in 4pzH to 114° in 4pzH-Pyr1), and therefore supporting the long theoretical half-life through Z-ground state stabilization (Table 1). However, for the highly congested doubly