Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines

• Camila B. Francisco,
• Cleverton S. Fernandes,
• Ulisses Z. de Melo,
• Roberto Rittner,
• Gisele F. Gauze and
• Ernani A. Basso

Beilstein J. Org. Chem. 2019, 15, 818–829, doi:10.3762/bjoc.15.79

• competition of interactions, with regard to their volumes and steric repulsions, and the particular effects of the solvation medium on them, besides the intrinsic stereoelectronic effects. The sum of these factors in a system may lead to results different from those expected by considering just simple

• methanol-d4. The conformational preference was affected neither by the solvent polarity nor the halogen size, suggesting the presence of strong stereoelectronic effects being responsible for the conformational behavior in these systems. Theoretical calculations are in agreement with experimental data, the

Influence of per-O-sulfation upon the conformational behaviour of common furanosides

• Alexey G. Gerbst,
• Vadim B. Krylov,
• Dmitry A. Argunov,
• Maksim I. Petruk,
• Arsenii S. Solovev,
• Andrey S. Dmitrenok and
• Nikolay E. Nifantiev

Beilstein J. Org. Chem. 2019, 15, 685–694, doi:10.3762/bjoc.15.63

• distortion of the pyranoside ring [1][2], which strongly modifies the chemical behaviour of the pyranoside substrate by influencing the spatial environment of the reaction center and changing stereoelectronic effects [3][4][5]. A rather complex case is observed for sulfate groups; in addition to van der

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst

• Kimihiro Komeyama,
• Shunsuke Sakiyama,
• Kento Iwashita,
• Itaru Osaka and
• Ken Takaki

Beilstein J. Org. Chem. 2018, 14, 1413–1420, doi:10.3762/bjoc.14.118

• converted to vinylchromium, which would be inactive in the oligomerization, but is a highly nucleophilic species. According to these findings, the reversed diastereoselectivity in Scheme 9 might be due to stereoelectronic effects [21][22]. Thus, the σ*(C–O) bond stabilizes the forming σ(Co–C) bond in the

Conformational preferences of α-fluoroketones may influence their reactivity

• Graham Pattison

Beilstein J. Org. Chem. 2017, 13, 2915–2921, doi:10.3762/bjoc.13.284

• , supported by computation, that this effect is due to reactive conformations in which the C–X bond is orthogonal to the carbonyl group for good orbital overlap being disfavoured in the case of fluoro ketones. Keywords: α-halogenated ketones; conformational analysis; reactivity; stereoelectronic effects

Conformational impact of structural modifications in 2-fluorocyclohexanone

• Francisco A. Martins,
• Josué M. Silla and
• Matheus P. Freitas

Beilstein J. Org. Chem. 2017, 13, 1781–1787, doi:10.3762/bjoc.13.172

• organofluorine compounds affects conformational properties, since it can induce stereoelectronic effects, such as σC–H to σ*C–F hyperconjugative interactions in case of an antiparallel oriented C–H bond. This is the origin of the so-called 'gauche effect', because electronegative C–X bonds do not participate in

The reductive decyanation reaction: an overview and recent developments

• Jean-Marc R. Mattalia

Beilstein J. Org. Chem. 2017, 13, 267–284, doi:10.3762/bjoc.13.30

• decyanation reaction depends on the structure of the α-aminonitrile, stereoelectronic effects and internal strain of the molecule [68]. Chuang et al. prepared a set of α-aminoacrylonitriles 11 by a cyano-promoted aza-Diels–Alder cycloaddition [71]. The cyano groups were then removed in high yields by

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

• Mikael Bols and
• Christian Marcus Pedersen

Beilstein J. Org. Chem. 2017, 13, 93–105, doi:10.3762/bjoc.13.12

• piperidinium ion is a measure of the stereoelectronic effects and correlates with the glycosyl donor’s reactivity observed. Forcing an OR group from an equatorial position into an axial position by, e.g., a bulky silyl group, increases the basicity of the piperidines, which is analogous to increasing the

Stereoselective synthesis of fused tetrahydroquinazolines through one-pot double [3 + 2] dipolar cycloadditions followed by [5 + 1] annulation

• Xiaofeng Zhang,
• Kenny Pham,
• Shuai Liu,
• Marc Legris,
• Alex Muthengi,
• Jerry P. Jasinski and
• Wei Zhang

Beilstein J. Org. Chem. 2016, 12, 2204–2210, doi:10.3762/bjoc.12.211

• ). Compound 7b was an exception, which was obtained in a trace amount. It was found that replacing maleimides 6 with other activated alkenes such as dimethyl maleate, benzoquinone, naphthalene-1,4-dione, and maleonitrile failed to afford products 7q–t, probably due to unfavorable stereoelectronic effects

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• . Conclusion Many of the early examples of bridged-polycycle synthesis via C–H bond insertion arose from strategies targeting the total synthesis of natural products. The results of these early efforts led to useful reaction conditions, a better understanding of stereoelectronic effects involved in the

New metathesis catalyst bearing chromanyl moieties at the N-heterocyclic carbene ligand

• Agnieszka Hryniewicka,
• Szymon Suchodolski,
• Agnieszka Wojtkielewicz,
• Jacek W. Morzycki and
• Stanisław Witkowski

Beilstein J. Org. Chem. 2015, 11, 2795–2804, doi:10.3762/bjoc.11.300

• previously reported a few catalysts bearing the chromanyl moiety, derived from vitamin E [21][22][23]. In such a system as 2,2,5,7,8-pentamethyl-6-hydroxychromane (α-tocopherol model compound) specific stereoelectronic effects are observed [24][25], which might improve the activity of the catalyst bearing

• chromanyl moieties symmetrically N,N’-disubstituted in the imidazolinium ring (9, Figure 2). According to Smith et al. [26] α-tocopherol and its amino analogue (α-tocopheramine) have comparable properties, coming from the same stereoelectronic effects mentioned above [24][25]. We expected that these effects

• carbene [Ru]=CHCOX, which is kinetically favourable. As a result, a stronger electron-donating ligand should stabilise the electron-deficient enoic carbene [31]. One can speculate that specific stereoelectronic effects occurring in the chromanyl system, known from the vitamin E chemistry, contribute to

Investigation of the role of stereoelectronic effects in the conformation of piperidones by NMR spectroscopy and X-ray diffraction

• Cesar Garcias-Morales,
• David Ortegón-Reyna and
• Armando Ariza-Castolo

Beilstein J. Org. Chem. 2015, 11, 1973–1984, doi:10.3762/bjoc.11.213

• a chair–boat conformation, while those in 2,4-diphenyl-3-azabicyclo[3.3.1]nonan-9-ones, compounds 3–8, adopt a chair–chair conformation because of stereoelectronic effects. These stereoelectronic effects were analyzed by the 1JC–H coupling constants, which were measured in the 13C satellites of the

• 1H NMR spectra obtained with the hetero-dqf pulse sequence. In the solid state, these stereoelectronic effects were investigated by measurement of X-ray diffraction data, the molecular geometry (torsional bond angles and bond distances), and inter- and intramolecular interactions, and by natural bond

• –H(7)eq), a type of hyperconjugative interaction. Keywords: NMR spectroscopy; piperidone; spin–spin coupling constant; stereoelectronic effect; X-ray diffraction structure; Introduction Stereoelectronic effects have attracted the attention of many researchers with an interest in organic chemistry

Natural phenolic metabolites with anti-angiogenic properties – a review from the chemical point of view

• Qiu Sun,
• Jörg Heilmann and
• Burkhard König

Beilstein J. Org. Chem. 2015, 11, 249–264, doi:10.3762/bjoc.11.28

• the two aromatic rings was shortened, and a series of compounds (Scheme 2) with different substitutions on the aromatic rings was synthesized to explore the role of stereoelectronic effects. It was demonstrated that these analogs of curcumin showed excellent anti-angiogenic activity with equivalent or

Design and synthesis of novel bis-annulated caged polycycles via ring-closing metathesis: pushpakenediol

• Sambasivarao Kotha and
• Mirtunjay Kumar Dipak

Beilstein J. Org. Chem. 2014, 10, 2664–2670, doi:10.3762/bjoc.10.280

• combination with the RCM reaction provides a useful strategy for the synthesis of novel and intricate molecular frameworks such as 22, which is suitable for studying stereoelectronic effects [43]. The strategy shown here is an atom economical process. The synthetic sequence opens up a new route to complex

De novo macrolide–glycolipid macrolactone hybrids: Synthesis, structure and antibiotic activity of carbohydrate-fused macrocycles

• Richard T. Desmond,
• Anniefer N. Magpusao,
• Chris Lorenc,
• Jeremy B. Alverson,
• Nigel Priestley and
• Mark W. Peczuh

Beilstein J. Org. Chem. 2014, 10, 2215–2221, doi:10.3762/bjoc.10.229

• , stereogenic centers and stereoelectronic effects combine to dictate the “topology” or overall fold of a macrocycle. The structure of β-D-galactose-[13]-macrodiolide 3 [9], derived from X-ray data, originated this line of investigation. It showed that both esters and the epoxide unit are each composed of four

• this case the macrocyclic ring. In total it is the balancing of a number of small factors such as rigidification by multi-atom planar units, absolute configuration of stereogenic centers and stereoelectronic effects that dictate the observed structures. Minimum inhibitory concentrations (MICs) against

Application of cyclic phosphonamide reagents in the total synthesis of natural products and biologically active molecules

• Thilo Focken and
• Stephen Hanessian

Beilstein J. Org. Chem. 2014, 10, 1848–1877, doi:10.3762/bjoc.10.195

• enantioselectivities. The attack of electrophiles E is favored from the “left cleft” of the anion 29 in the (R,R)-isomer due to steric and stereoelectronic effects. Intermediates such as 30 can be isolated and purified as crystalline solids suitable for X-ray analysis if water is used for quenching instead of acetic

Stereodivergent synthesis of jaspine B and its isomers using a carbohydrate-derived alkoxyallene as C₃-building block

• Volker M. Schmiedel,
• Stefano Stefani and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2013, 9, 2564–2569, doi:10.3762/bjoc.9.291

• -azidotetrahydrofuranols rac-9 and rac-10 in a satisfying yield of 62% over two steps (Scheme 4). Only the two diastereomers shown in Scheme 4 were isolated, whereas the two other possible isomers could not be detected. The obtained diastereoselectivity of the reduction is likely due to stereoelectronic effects of the α

Acceptor-influenced and donor-tuned base-promoted glycosylation

• Stephan Boettcher,
• Martin Matwiejuk and
• Joachim Thiem

Beilstein J. Org. Chem. 2012, 8, 413–420, doi:10.3762/bjoc.8.46

• -glycopyranosides. The considerable effect of the anomeric configuration on the reactivity of remote hydroxy groups may be rationalized by stereoelectronic effects [12]. Moreover, the lower reactivities of the methyl β-glycopyranosides may also be dependent on the decreased solubility of the partially deprotonated

Carbasugar analogues of galactofuranosides: α-O-linked derivatives

• Jens Frigell and
• Ian Cumpstey

Beilstein J. Org. Chem. 2010, 6, 1127–1131, doi:10.3762/bjoc.6.129

• -membered ring series, irrespective of the preferred envelope conformation of the epoxide, and that stereoelectronic effects are thus likely to be much less relevant for the more flexible cyclopentane derivatives. One factor that could speak against good regioselectivity in this case would be the fact that

Novel tetracyclic structures from the synthesis of thiolactone-isatin hybrids

• Renate Hazel Hans,
• Hong Su and
• Kelly Chibale

Beilstein J. Org. Chem. 2010, 6, No. 78, doi:10.3762/bjoc.6.78

• ′-substituted tetracycles (Table 1 and Table 2). This drawback can most likely be ascribed to entropy factors and stereoelectronic effects [45][46][47][48]. The structures of the tetracycles 4 were unambiguously assigned by single crystal X-ray crystallographic analysis. Single crystals for 4a–c were obtained

The C–F bond as a conformational tool in organic and biological chemistry

• Luke Hunter

Beilstein J. Org. Chem. 2010, 6, No. 38, doi:10.3762/bjoc.6.38

• ; stereoelectronic effects; Review General aspects of the C–F bond Fluorine is a small atom, with an atomic radius intermediate between that of hydrogen and oxygen (Table 1). The small size of fluorine means that it can be incorporated into an organic molecule as a replacement for hydrogen without dramatically

• fluoroalkane” (e.g. 54, Figure 12), which is conceptually intermediate between alkanes and perfluoroalkanes [37]. Multi-vicinal fluoroalkanes are interesting systems for studying stereoelectronic effects such as the gauche effect and they also have potential applications in materials science, for example, as

• reported in due course. Conclusion The conformations of organofluorine compounds are influenced by a number of stereoelectronic effects associated with the C–F bond, including dipole–dipole interactions, charge–dipole interactions and hyperconjugation. Knowledge of these conformational effects allows the