Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

Catalysis of linear alkene metathesis by Grubbs-type ruthenium alkylidene complexes containing hemilabile α,α-diphenyl-(monosubstituted-pyridin-2-yl)methanolato ligands

• Tegene T. Tole,
• Johan H. L. Jordaan and
• Hermanus C. M. Vosloo

Beilstein J. Org. Chem. 2019, 15, 194–209, doi:10.3762/bjoc.15.19

• ligand, and that was to focus on substituents on the α-carbon of the ligand. To our knowledge, there are no reports on investigations of electronic and/or steric effect(s) of pyridinyl substituents on the chelation efficiency of pyridinyl alcoholato ligands, and subsequently its metathesis activity

• electron-donation by the methyl group cannot significantly influence the electron density on the pyridine nitrogen. There is also no steric effect that would interfere with the Ru–N bond strength. The strengthening effect on the Ru–N chelation would, therefore, possibly be low compared to the other

• to hemilability than 6 and exhibits higher activity. Therefore, for 4-Me- and 5-Me-subtstituted precatalysts, only the inductive electron-donation effect of the methyl group is the reason for the increased stability. In the 3-Me- and 3-OMe-substituted precatalysts, however, the steric effect and

Hydroarylations by cobalt-catalyzed C–H activation

• Rajagopal Santhoshkumar and
• Chien-Hong Cheng

Beilstein J. Org. Chem. 2018, 14, 2266–2288, doi:10.3762/bjoc.14.202

• amines, and silyl alkynes in the presence of CoCp*(CO)I2 catalyst gave uncommon branched-selective products 16 in good yields with reasonable selectivity (Scheme 12) [56]. DFT calculations indicated that the regioselectivity of silyl alkynes was controlled by its steric effect in the protonolysis step

• , whereas the IPr·HCl ligand provided tetrahydropyridoindoles 31 in reasonable regioselectivity (Scheme 22) [70]. Remarkably, the regioselectivity of the reaction is not only controlled by the steric effect of NHC ligand, but also depends on the olefin tether in 29. Recently, Petit and co-workers also

Synthesis of 1,4-imino-L-lyxitols modified at C-5 and their evaluation as inhibitors of GH38 α-mannosidases

• Maroš Bella,
• Sergej Šesták,
• Ján Moncoľ,
• Miroslav Koóš and
• Monika Poláková

Beilstein J. Org. Chem. 2018, 14, 2156–2162, doi:10.3762/bjoc.14.189

• was decreasing with increasing size of this functional group, suggesting a certain role of steric effect. An even smaller effect was found for 4-halogenation of the N-benzyl substituent, arguing against a steric or electron effect at this position of the phenyl ring. Nevertheless, the synthesis of

Enzyme-free genetic copying of DNA and RNA sequences

• Marilyne Sosson and
• Clemens Richert

Beilstein J. Org. Chem. 2018, 14, 603–617, doi:10.3762/bjoc.14.47

• , in extension buffer containing 80 mM MgCl2, were typically found to be in the range of 5–8 h at a pH of 8.9, both for ribonucleotides and for deoxynucleotides. Only OAt-dTMP was slower to hydrolyze, with a t1/2 of 16 h [28]. Molecular modeling suggested that this may be due to the steric effect of

Binding abilities of a chiral calix[4]resorcinarene: a polarimetric investigation on a complex case of study

• Marco Russo and
• Paolo Lo Meo

Beilstein J. Org. Chem. 2017, 13, 2698–2709, doi:10.3762/bjoc.13.268

• considered separately. This suggests that the conformational and dynamic restrictions consequent to inclusion may be due to the occurrence of specific host–guest interactions rather than to a mere steric effect. In order to clarify the latter point, we investigated the possible structure of the complexes

Diastereoselective Mannich reactions of pseudo-C₂-symmetric glutarimide with activated imines

• Tatsuya Ishikawa,
• Tomoko Kawasaki-Takasuka,
• Toshio Kubota and
• Takashi Yamazaki

Beilstein J. Org. Chem. 2017, 13, 2473–2477, doi:10.3762/bjoc.13.244

• general trend, LiHMDS tended to afford lower chemical yields the reason for which was not clear at present. Imines from aliphatic aldehydes 2hc and 2ic could be used in a similar manner but the steric effect due to the branched structure in the latter affected the reaction to some extent (Table 2, entries

Development of a method for the synthesis of 2,4,5-trisubstituted oxazoles composed of carboxylic acid, amino acid, and boronic acid

• Kohei Yamada,
• Naoto Kamimura and
• Munetaka Kunishima

Beilstein J. Org. Chem. 2017, 13, 1478–1485, doi:10.3762/bjoc.13.146

• yield of 71% (Table 3, entry 6), whereas reactions of the o-tolyl group resulted in moderate yields under both conditions owing to the steric effect (Table 3, entries 7 and 8). The reaction with 3-thienylboronic acid (4g) under conditions B proceeded to give 5aag in 68% yield (Table 3, entries 9 and 10

A practical and efficient approach to imidazo[1,2-a]pyridine-fused isoquinolines through the post-GBB transformation strategy

• Taofeng Shao,
• Zhiming Gong,
• Tianyi Su,
• Wei Hao and
• Chao Che

Beilstein J. Org. Chem. 2017, 13, 817–824, doi:10.3762/bjoc.13.82

• -ethynylbenzaldehydes 2 and tert-butylisocyanide (3). Indeed, the acetylene group in the aldehyde component had no obvious steric effect on the efficiency of the GBB reaction affording the GBB product in good to excellent yields in most cases. On the other hand, the substituent ortho to the amino group in the amidine

Synthesis and optical properties of new 5'-aryl-substituted 2,5-bis(3-decyl-2,2'-bithiophen-5-yl)-1,3,4-oxadiazoles

• Anastasia S. Kostyuchenko,
• Tatyana Yu. Zheleznova,
• Anton J. Stasyuk,
• Aleksandra Kurowska,
• Wojciech Domagala,
• Adam Pron and
• Alexander S. Fisyuk

Beilstein J. Org. Chem. 2017, 13, 313–322, doi:10.3762/bjoc.13.34

• 88°) [29]. This dihedral angle is “a compromise” between the conjugation of the adjacent segments which favors the molecule’s planarity and steric hindrance effects which induce torsion. In the case of larger sized substituents, the steric effect predominates leading to large values of dihedral

Microwave-assisted cyclizations promoted by polyphosphoric acid esters: a general method for 1-aryl-2-iminoazacycloalkanes

• Jimena E. Díaz,
• María C. Mollo and
• Liliana R. Orelli

Beilstein J. Org. Chem. 2016, 12, 2026–2031, doi:10.3762/bjoc.12.190

• 7 in good to high yields (Table 5). A clear steric effect on the reactivity was observed in the case of compound 7g (Table 5, entry 7), which resulted in low conversion of the substrate. Conclusion In summary, we have developed a straightforward and efficient protocol for the microwave-assisted

Practical synthetic strategies towards lipophilic 6-iodotetrahydroquinolines and -dihydroquinolines

• David R. Chisholm,
• Garr-Layy Zhou,
• Ehmke Pohl,
• Roy Valentine and
• Andrew Whiting

Beilstein J. Org. Chem. 2016, 12, 1851–1862, doi:10.3762/bjoc.12.174

• 88% yields according to 1H NMR analysis of the crude mixtures. Addition of an N-alkyl group to supplement the steric effect of the benzylic phenyl (N–Me, 23b) resulted in the reaction favouring the production of the DHQ 25b (62%) over the THQ 24b (38%). Retaining the N-alkyl group whilst removing the

• steric effect of this benzylic phenyl group (23d) now switched the preference of the reaction towards the THQ 24d (63%) compared to DHQ 25d (21%). In contrast to the clean conversions of the other quinolin-2-ones, crude 1H NMR analysis of the DIBAL reduction of 23d indicated a variety of side products

One-pot synthesis of tetracyclic fused imidazo[1,2-a]pyridines via a three-component reaction

• Bo Yang,
• Chuanye Tao,
• Taofeng Shao,
• Jianxian Gong and
• Chao Che

Beilstein J. Org. Chem. 2016, 12, 1487–1492, doi:10.3762/bjoc.12.145

• [36]. Results and Discussion It is noteworthy that there was no report on a ketone-involving GBB reaction, and several attempts to explore the GBB reaction utilizing ketones as carbonyl reactant failed [27][37]. These difficulties could be partially explained in terms of the electronic and steric

• effect of the ketone involved. More importantly, when a ketone is used in the reaction the formed unstable [4 + 1] cycloaddition adduct could not undergo a [1,3]-alkyl shift. On the other hand the reaction with an aldehyde allows further conversion through a [1,3]-hydride shift to form a stable and

Is conformation a fundamental descriptor in QSAR? A case for halogenated anesthetics

• Maria C. Guimarães,
• Mariene H. Duarte,
• Josué M. Silla and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2016, 12, 760–768, doi:10.3762/bjoc.12.76

• Pauling's electronegativity (ε) scale, since polar properties should help to modulate their mode of interaction with an enzyme (see Table 5 for correspondence of ε with pixel values and approximate colors). Another useful parameter ruling bioactivity is the steric effect, which was accounted for by

Effective in silico prediction of new oxazolidinone antibiotics: force field simulations of the antibiotic–ribosome complex supervised by experiment and electronic structure methods

• Jörg Grunenberg and
• Giuseppe Licari

Beilstein J. Org. Chem. 2016, 12, 415–428, doi:10.3762/bjoc.12.45

• destabilized by nearly 70 kJ/mol in comparison with the guest 20. The increased steric effect is once again rising the energy of the complex and pushing the ligand outside the binding site. Conclusion The proposed combination of computational power and chemical intuition led to the prediction of several new

Co-solvation effect on the binding mode of the α-mangostin/β-cyclodextrin inclusion complex

• Chompoonut Rungnim,
• Sarunya Phunpee,
• Manaschai Kunaseth,
• Supawadee Namuangruk,
• Kanin Rungsardthong,
• Thanyada Rungrotmongkol and
• Uracha Ruktanonchai

Beilstein J. Org. Chem. 2015, 11, 2306–2317, doi:10.3762/bjoc.11.251

• , the steric effect of the α-MGS functional groups influences only the inclusion geometry, but not the binding energy. Further details for MD simulations of the α-MGS/βCD inclusion complex in water solvation system appear in Supporting Information File 1. Solvation effect on the α-MGS/β-CD inclusion

Supramolecular chemistry: from aromatic foldamers to solution-phase supramolecular organic frameworks

• Zhan-Ting Li

Beilstein J. Org. Chem. 2015, 11, 2057–2071, doi:10.3762/bjoc.11.222

• and aliphatic ammonium and, at high concentrations in chloroform, a chiral aliphatic ammonium induced 23 to produce helicity bias. One important difference between fluorine and alkoxy groups is that fluorine does not cause a steric effect on aromatic stacking. Zeng and co-workers demonstrated this

Stereochemistry of ring-opening/cross metathesis reactions of exo- and endo-7-oxabicyclo[2.2.1]hept-5-ene-2-carbonitriles with allyl alcohol and allyl acetate

• Piotr Wałejko,
• Michał Dąbrowski,
• Lech Szczepaniak,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 1893–1901, doi:10.3762/bjoc.11.204

• -tolyl substituted NHC ligand in [Ru]5 exerts a smaller steric effect than the -PCy3 residue in [Ru]1–4. Furthermore, the bulky phosphine ligand (PCy3) expands away from the transition metal center (coordination sphere), while the N,N’-o-tolyl substituent attached to the central imidazole ring penetrates

Qualitative evaluation of regioselectivity in the formation of di- and tri-6-O-tritylates of α-cyclodextrin

• Keisuke Yoshikiyo,
• Yoshihisa Matsui and
• Tatsuyuki Yamamoto

Beilstein J. Org. Chem. 2015, 11, 1530–1540, doi:10.3762/bjoc.11.168

• evaluate quantitiatively the steric effect of the bulky trityl group on the regioselectivity of the reaction. For the sake of clarity, it must be noted here that letters from A to F that identify individual glucopyranose units are numbered along with the α1→4 linkage direction, and that the term “clockwise

Antioxidant potential of curcumin-related compounds studied by chemiluminescence kinetics, chain-breaking efficiencies, scavenging activity (ORAC) and DFT calculations

• Adriana K. Slavova-Kazakova,
• Silvia E. Angelova,
• Timur L. Veprintsev,
• Petko Denev,
• Davide Fabbri,
• Maria Antonietta Dettori,
• Maria Kratchanova,
• Vladimir V. Naumov,
• Aleksei V. Trofimov,
• Rostislav F. Vasil’ev,
• Giovanna Delogu and
• Vessela D. Kancheva

Beilstein J. Org. Chem. 2015, 11, 1398–1411, doi:10.3762/bjoc.11.151

• higher ID than monomer 5). These results may be rationalized in terms of the steric effect of the longer side chain in monomer 4, which leads to a lower level of side reactions of the pertinent phenoxyl radicals. Monomers 2, 3 and 5 demonstrated similar antioxidant efficiencies (PF). However, they differ

An unusually stable chlorophosphite: What makes BIFOP–Cl so robust against hydrolysis?

• Roberto Blanco Trillo,
• Jörg M. Neudörfl and
• Bernd Goldfuss

Beilstein J. Org. Chem. 2015, 11, 313–322, doi:10.3762/bjoc.11.36

• large steric demand of encapsulating fenchane units renders the phosphorus atom nearly inaccessible by nucleophilic reagents, but only for BIFOP–Cl. In addition to the steric effect, a hypervalent P(III)–O interaction as well as an electronic conjugation effect causes the high reactivity of O–BIFOP–Cl

• hydrolysis, O–BIFOP–Cl (3) reacts instantly with water, leading to cyclofenchene 6. X-ray studies revealed that the increased reactivity of the intermediate carbenium ion and cyclopropane formation is due to a steric effect caused by the shielding of the fenchane groups and a hypervalent P(III)–O interaction

Three-component synthesis of C₂F₅-substituted pyrazoles from C₂F₅CH₂NH₂·HCl, NaNO₂ and electron-deficient alkynes

• Pavel K. Mykhailiuk

Beilstein J. Org. Chem. 2015, 11, 16–24, doi:10.3762/bjoc.11.3

• the isomer 19b with EWG at the 4th position, violating the orbital symmetry rules (Figure 3 and Figure 4). Presumably, the steric repulsion between bulky C2F5 and SiMe3 groups forced the reaction to follow the reversed regioselectivity – the steric effect has overcompensated the electronic one (Figure

• . In compounds 13–15 the steric effect overcompensated the electronic one, but the impact of steric effect decreased with increasing the size of the second substituent: CH3CO (19), ClCH2CO (20), HF2CCO (21) increasing the percentage of α-isomers (0% in 19b, 20% in 20a/b, 28% in 21a/b). Reactivity of

• reaction with C2F5CHN2 reached only 52% conversion. Obviously, the steric effect overcompensated the electronic one; and C2F5CHN2 was less active than CF3CHN2 (Scheme 1). Another factor, however, must be kept in mind while comparing the reactivities of C2F5CHN2 and CF3CHN2: the reactions of C2F5CHN2 can be

Synthesis of divalent ligands of β-thio- and β-N-galactopyranosides and related lactosides and their evaluation as substrates and inhibitors of Trypanosoma cruzi trans-sialidase

• María Emilia Cano,
• Rosalía Agusti,
• Alejandro J. Cagnoni,
• María Florencia Tesoriero,
• José Kovensky,
• María Laura Uhrig and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2014, 10, 3073–3086, doi:10.3762/bjoc.10.324

• and 120 min gave very similar results (not shown). A steric effect operating on the sialylation of multiple Galp residues has been previously suggested for lactosyl lipids attached to membrane microdomains [40]. The dependence of the amount of disialylation of the divalent glycans on the concentration

Stereoselective synthesis of perillaldehyde-based chiral β-amino acid derivatives through conjugate addition of lithium amides

• Zsolt Szakonyi,
• Reijo Sillanpää and
• Ferenc Fülöp

Beilstein J. Org. Chem. 2014, 10, 2738–2742, doi:10.3762/bjoc.10.289

• subsequently converted to the tert-butyl ester (3) [37]. In order to study the steric effect of the more bulky isopropyl group on the Michael addition, (4S)-tert-butyl phellandrate (6) was prepared via (4S)-phellandral (4) and (4S)-phellandric acid (5) (Scheme 1) [38][39][40]. The asymmetric Michael addition

• -butyl perillate (3), however the saturation of the isopropenyl function at position 4 proved to have no effect on the stereoselectivity of the reaction (Scheme 3). When N-benzyl-N-α-methylbenzylamine was applied as a chiral nucleophile in the conjugate addition, the steric effect of the α-methyl

Chiral phosphines in nucleophilic organocatalysis

• Yumei Xiao,
• Zhanhu Sun,
• Hongchao Guo and
• Ohyun Kwon

Beilstein J. Org. Chem. 2014, 10, 2089–2121, doi:10.3762/bjoc.10.218

• functionalized cyclopentenes in moderate yields with moderate to high enantioselectivities (Scheme 19) [50]. The presence of a trimethylsilyl group at the α-position of the allenone was key to achieving a regioselective [3 + 2] annulation. This remarkable steric effect probably suppressed the [4 + 2] self