cis–trans Isomerization of silybins A and B

• Michaela Novotná,
• Radek Gažák,
• David Biedermann,
• Florent Di Meo,
• Petr Marhol,
• Marek Kuzma,
• Lucie Bednárová,
• Kateřina Fuksová,
• Patrick Trouillas and
• Vladimír Křen

Beilstein J. Org. Chem. 2014, 10, 1047–1063, doi:10.3762/bjoc.10.105

• be explained either by a solvent effect or by the participation of the acetyl group. However, the second possibility is less probable, since the participation of the acetyl group should lead to the formation of an isomer with a retained configuration at C-11 (two subsequent nucleophilic substitutions

• character, which partially rationalizes the solvent effect observed here. Conclusion We report here the first syntheses of hitherto undescribed cis-isomers of silybin in optically pure form starting from silybin A (1a) and B (1b). The determination of their absolute configuration was based on an analysis of

Substrate dependent reaction channels of the Wolff–Kishner reduction reaction: A theoretical study

• Shinichi Yamabe,
• Guixiang Zeng,
• Wei Guan and
• Shigeyoshi Sakaki

Beilstein J. Org. Chem. 2014, 10, 259–270, doi:10.3762/bjoc.10.21

• investigated by density functional theory calculations. The B3LYP [38][39] method was used. The basis set employed was 6-311+G(d,p). Geometry optimizations and vibrational analyses were carried out in the solution phase. Here, 1,2-ethanediol (ethylene glycol, HO–CH2–CH2–OH) was used as the solvent. The solvent

• effect was considered by the polarizable continuum model (PCM) [40][41][42]. Geometries of transition states (TSs) were determined by the input data consisting of two steps. For the first step, the initial geometry containing average and assumed distances between covalent and intermolecular interactions

3-Pyridinols and 5-pyrimidinols: Tailor-made for use in synergistic radical-trapping co-antioxidant systems

• Luca Valgimigli,
• Daniele Bartolomei,
• Riccardo Amorati,
• Evan Haidasz,
• Jason J. Hanthorn,
• Susheel J. Nara,
• Johan Brinkhorst and
• Derek A. Pratt

Beilstein J. Org. Chem. 2013, 9, 2781–2792, doi:10.3762/bjoc.9.313

• synergism we observed (vide infra). The results demonstrate a significant kinetic solvent effect, which was most pronounced for the least reactive compounds. For example, kinh for the methoxy-substituted pyridinol 5a dropped by a factor of 18 on going from chlorobenzene to acetonitrile, while the reactivity

• -fold. Ingold has clearly demonstrated that formal H-atom transfer reactions of the type X–H + Y• → X• + H–Y, where X is an electronegative atom, can experience a large kinetic solvent effect (KSE). In fact, these reactions are slowed down in hydrogen-bond accepting (HBA) solvents as a result of H-bond

Garner’s aldehyde as a versatile intermediate in the synthesis of enantiopure natural products

• Mikko Passiniemi and
• Ari M.P. Koskinen

Beilstein J. Org. Chem. 2013, 9, 2641–2659, doi:10.3762/bjoc.9.300

• carbonyl groups, thus causing the Felkin–Anh control. When the steric bulk of the nucleophile was increased from PhMgBr to iPrMgBr the selectivity reversed from 5:1 anti/syn to 1:6 with iPrMgBr. A distinct solvent effect was also observed (Scheme 11). The selectivity obtained by Joullie for the reaction of

Copper-catalyzed trifluoromethylation of alkenes with an electrophilic trifluoromethylating reagent

• Xiao-Ping Wang,
• Jin-Hong Lin,
• Cheng-Pan Zhang,
• Ji-Chang Xiao and
• Xing Zheng

Beilstein J. Org. Chem. 2013, 9, 2635–2640, doi:10.3762/bjoc.9.299

• desired conversion either. The examination of the solvent effect showed that the solvent is quite important for the reaction (Table 1, entries 16–20). When the reaction was carried out in DMF, the expected product 2a was obtained in excellent yield (Table 1, entry 16). The yield was decreased dramatically

Studies on the photodegradation of red, green and blue phosphorescent OLED emitters

• Susanna Schmidbauer,
• Andreas Hohenleutner and
• Burkhard König

Beilstein J. Org. Chem. 2013, 9, 2088–2096, doi:10.3762/bjoc.9.245

• photostabilities of the red and blue emitter and the solvent effect is therefore negligible. With the overall higher stabilities of compounds that emit green light however, processes associated with CH2Cl2 as the solvent become apparent. LC–MS analysis indeed revealed that the main observed degradation products of

Bioinspired total synthesis of katsumadain A by organocatalytic enantioselective 1,4-conjugate addition

• Yongguang Wang,
• Ruiyang Bao,
• Shengdian Huang and
• Yefeng Tang

Beilstein J. Org. Chem. 2013, 9, 1601–1606, doi:10.3762/bjoc.9.182

• additive, p-nitrobenzoic acid (PNBA) was found to afford 5a in an excellent yield, but with a decreased ee value (80%). Furthermore, the solvent effect was also examined. Among the several solvents examined, both MeOH and DMSO proved to be suitable solvent systems (Table 1, entries 6 and 8) by furnishing

Diastereoselective synthesis of nitroso acetals from (S,E)-γ-aminated nitroalkenes via multicomponent [4 + 2]/[3 + 2] cycloadditions promoted by LiCl or LiClO₄

• Leandro Lara de Carvalho,
• Robert Alan Burrow and
• Vera Lúcia Patrocinio Pereira

Beilstein J. Org. Chem. 2013, 9, 838–845, doi:10.3762/bjoc.9.96

• diffraction experiment. Keywords: chiral heterodiene; hetero-Diels–Alder reaction; pyrrolizidin-3-one; solvent effect; tandem reaction; Introduction Conjugated nitroalkenes play an important role in cycloaddition reactions providing useful nitrogenated cycloadducts with varied synthetic applications (Scheme

• -diamines [19]. Herein, we report the reactivity and diastereoselectivity of 5a–c as heterodienes in a multicomponent [4 + 2]/[3 + 2] cycloaddition with ethyl vinyl ether (EVE) and selected electron-deficient alkenes in the presence of LiCl or LiClO4 as promoters. A study on the solvent effect was also

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• their character as local minima or transition structures. IRC calculations were performed in order to validate the connection of each transition state with the respective reactants and products. The solvent effect was computed by carrying out the single-point energy calculations of the gas-phase

Theoretical study on β-cyclodextrin inclusion complexes with propiconazole and protonated propiconazole

• Adrian Fifere,
• Narcisa Marangoci,
• Stelian Maier,
• Adina Coroaba,
• Dan Maftei and
• Mariana Pinteala

Beilstein J. Org. Chem. 2012, 8, 2191–2201, doi:10.3762/bjoc.8.247

• heat of formation, after the removal of water molecules. A full optimization of the equilibrium geometries after removing water molecules would have led to a complete loss of information concerning the solvent effect. Schematic representation of the β-cyclodextrin (a) and propiconazole (b) molecules

Synthesis and evaluation of new guanidine-thiourea organocatalyst for the nitro-Michael reaction: Theoretical studies on mechanism and enantioselectivity

• Tatyana E. Shubina,
• Matthias Freund,
• Sebastian Schenker,
• Timothy Clark and
• Svetlana B. Tsogoeva

Beilstein J. Org. Chem. 2012, 8, 1485–1498, doi:10.3762/bjoc.8.168

• the further optimization at the B3PW91/6–31G(d) level. Conformer 7a is the only one with two hydrogen bonds between a nitrogen atom in the guanidine moiety and hydrogen atoms from the thiourea fragment. While inclusion of the solvent effect (DFT-PCM) gives a preference of 3.1 kcal·mol−1 for 7b over 7a

• Complex2a, which is less stable than Complex2 by up to 22.9 kcal·mol−1 (MP2, Scheme 4). Again, gas-phase DFT, MP and DFT-D results follow the same trend, while inclusion of the solvent effect makes Complex2a 0.4 kcal·mol−1 more stable than Complex2 (Scheme 4). In this complex, malonate 14 is coordinated

Cyclodextrin nanosponge-sensitized enantiodifferentiating photoisomerization of cyclooctene and 1,3-cyclooctadiene

• Wenting Liang,
• Cheng Yang,
• Masaki Nishijima,
• Gaku Fukuhara,
• Tadashi Mori,
• Andrea Mele,
• Franca Castiglione,
• Fabrizio Caldera,
• Francesco Trotta and
• Yoshihisa Inoue

Beilstein J. Org. Chem. 2012, 8, 1305–1311, doi:10.3762/bjoc.8.149

• photoisomerization mediated by conventional sensitizer-modified CDs [9], since the addition of alcohol simply reduces the guest affinity [46][47] and hence the ee of the product. This unusual solvent effect upon the addition of alcohol to the aqueous solution of CDNS reinforces the above hypothesis that the

Asymmetric organocatalytic decarboxylative Mannich reaction using β-keto acids: A new protocol for the synthesis of chiral β-amino ketones

• Chunhui Jiang,
• Fangrui Zhong and
• Yixin Lu

Beilstein J. Org. Chem. 2012, 8, 1279–1283, doi:10.3762/bjoc.8.144

• reaction (Table 1, entries 14 and 15). A screening of the solvent effect was then followed, and the results are summarized in Table 2. In general, the reaction proceeded very well in common aprotic solvents, and excellent yields were consistently obtained (Table 2, entries 1–9). Enantioselectivity of the

Recent advances towards azobenzene-based light-driven real-time information-transmitting materials

• Jaume García-Amorós and
• Dolores Velasco

Beilstein J. Org. Chem. 2012, 8, 1003–1017, doi:10.3762/bjoc.8.113

• time at 298 K, τ, for the azoderivative 4 (type-I) and the azophenol 10 (type-II). Solvent effect on the thermal relaxation time at 298 K, τ, for the type-II azophenols 11–13. Transient generated by irradiation with UV-light (λ = 355 nm) for the type-II azophenol 12 in ethanol (left) and changes in the

• azophenol 10 (type-II). Solvent effect on the thermal relaxation time at 298 K, τ, for the type-II ortho-substituted azophenols 14–16. Cooperative effect of the para- and ortho-hydroxyl groups in azophenol 17. Effect of the poly-hydroxylation of the azobenzene core on the thermal relaxation time at 298 K, τ

Enantioselective supramolecular devices in the gas phase. Resorcin[4]arene as a model system

• Caterina Fraschetti,
• Matthias C. Letzel,
• Antonello Filippi,
• Maurizio Speranza and
• Jochen Mattay

Beilstein J. Org. Chem. 2012, 8, 539–550, doi:10.3762/bjoc.8.62

• irreversible, bond with their target. The main advantage of a gaseous environment is the exclusion of any counterion and/or solvent effect, while at the same time the chemicophysical properties of the isolated system can be subtly studied. Finally, the application of the displacement-reaction methodology

Solvent- and ligand-induced switch of selectivity in gold(I)-catalyzed tandem reactions of 3-propargylindoles

• Estela Álvarez,
• Delia Miguel,
• Patricia García-García,
• Manuel A. Fernández-Rodríguez,
• Félix Rodríguez and
• Roberto Sanz

Beilstein J. Org. Chem. 2011, 7, 786–793, doi:10.3762/bjoc.7.89

• point it was unclear whether the observed change of selectivity in favor of the Nazarov product 4a was mainly a solvent effect, or if the nature of the ligand also exerted an influence on the selectivity. To clear up this point the initial catalyst [(Ph3P)AuCl/AgOTf] was revisited, and 1a was treated

An efficient and practical entry to 2-amido-dienes and 3-amido-trienes from allenamides through stereoselective 1,3-hydrogen shifts

• Ryuji Hayashi,
• John B. Feltenberger,
• Andrew G. Lohse,
• Mary C. Walton and
• Richard P. Hsung

Beilstein J. Org. Chem. 2011, 7, 410–420, doi:10.3762/bjoc.7.53

• ). There appears to be some solvent effect on the E/Z selectivity with more polar solvents providing the best ratio (Table 1, entries 2–4). In addition to thermal conditions, we screened several Brønsted acids at room temperature in order to investigate a milder condition. While PTSA resulted in poor E/Z

• the pro-E transition state (Scheme 4). A thermodynamically driven equilibration from (Z)- to (E)-enamide post-isomerization is a real possibility that cannot be ruled out, and the observed solvent effect on the (E/Z)-selectivity would particularly support this possible notion. An interesting discovery

Tribenzotriquinacenes bearing three peripheral or bridgehead urea groups stretched into the 3-D space

• Jörg Tellenbröker and
• Dietmar Kuck

Beilstein J. Org. Chem. 2011, 7, 329–337, doi:10.3762/bjoc.7.43

• 70% (11). Syntheses of tris-phenylurea-substituted tribenzotriquinacenes 5–7. Reagents and conditions: (i) PhNCO, CHCl3, 50 °C, 6 h, 84%. (ii) ditto, 86%. (iii) ditto, 96%. Solvent effect on the chemical shifts (δ) observed in the 1H NMR spectra (500 MHz) of the central (12d-) and the outer

pH-Responsive chromogenic-sensing molecule based on bis(indolyl)methene for the highly selective recognition of aspartate and glutamate

• Litao Wang,
• Xiaoming He,
• Yong Guo,
• Jian Xu and
• Shijun Shao

Beilstein J. Org. Chem. 2011, 7, 218–221, doi:10.3762/bjoc.7.29

• receptor 1 shifts to 435 nm as a result of the solvent effect (Figure 2b). Moreover, the absorption band at 435 nm decreases when the ratio of the acetonitrile to water reaches 4:6 (v/v), which is probably related to the solubility of 1. As a result, the amino acid recognition and sensing properties of 1

Donor-acceptor substituted phenylethynyltriphenylenes – excited state intramolecular charge transfer, solvatochromic absorption and fluorescence emission

• Ritesh Nandy and
• Sethuraman Sankararaman

Beilstein J. Org. Chem. 2010, 6, 992–1001, doi:10.3762/bjoc.6.112

• estimated from the electrochemical and spectral data for these derivatives. The HOMO and LUMO surfaces were obtained from DFT calculations. Keywords: charge transfer; fluorescence; solvatochromism; solvent effect; triphenylene; Introduction Fluorescent molecular probes that emit in the visible region and

• . Compared to 1a and 1b, the lowest energy absorption bands of 1c–g are further red shifted in both cyclohexane and acetonitrile. Although there is no significant solvent effect on the absorption bands of 1a–g in these two solvents, the lowest energy absorption bands are red shifted by 5–10 nm in cyclohexane

• of the energy of the dipole on the dielectric constant and refractive index of the solvent. The Lippert–Mataga equation accounts for the general solvent effect and does not account for specific solvent–fluorophore interactions, for example, through hydrogen bonding etc. The Lippert–Mataga plot for 1c

Concise methods for the synthesis of chiral polyoxazolines and their application in asymmetric hydrosilylation

• Wei Jie Li,
• Zun Le Xu and
• Sheng Xiang Qiu

Beilstein J. Org. Chem. 2010, 6, No. 29, doi:10.3762/bjoc.6.29

• temperature was optimized to −5 °C. As for solvent effect, the reaction displayed a preference for THF as solvent. The reaction proceeded very fast in CH3OH, but the ee was disappointingly low, only 55% (entry 4). However, 1-phenylethanol was obtained in high yield with high enantioselectivity in THF

Enantioselective nucleophilic difluoromethylation of aromatic aldehydes with Me₃SiCF₂SO₂Ph and PhSO₂CF₂H reagents catalyzed by chiral quaternary ammonium salts

• Chuanfa Ni,
• Fang Wang and
• Jinbo Hu

Beilstein J. Org. Chem. 2008, 4, No. 21, doi:10.3762/bjoc.4.21

• configuration [32]. From the above screening, the quaternary salts 6a and 8a derived from the CN and QN were selected as the catalysts for further study. Subsequently, the solvent effect was examined with catalyst 8a in the presence of solid KOH as the base at room temperature. It was shown that the use of