Search results

Search for "half-chair conformation" in Full Text gives 16 result(s) in Beilstein Journal of Organic Chemistry.

A versatile route towards 6-arylpipecolic acids

  • Erich Gebel,
  • Cornelia Göcke,
  • Carolin Gruner and
  • Norbert Sewald

Beilstein J. Org. Chem. 2025, 21, 1104–1115, doi:10.3762/bjoc.21.88

Graphical Abstract
  • accordance with coupling constants and resulting dihedral angles. Keywords: conformational restraints; dihedral angle NMR; half-chair conformation; modified amino acids; pipecolic acid; stereoselective hydrogenation; Suzuki–Miyaura cross-coupling; Introduction Non-proteinogenic amino acids play an
  • -S) and 3J(H2,H3,pro-R). Therefore, a half-chair conformation with ϕ(H2,H3,pro-S) = 90° and ϕ(H6,H5,pro-R) = 270° resulting in 3J(H2,H3,pro-S) = 3J(H6,H5,pro-R) ≈ 0 Hz and 3J(H2,H3,pro-R) = 5.0 Hz as well as 3J(H6,H5,pro-S) = 5.7 Hz (as shown in Figure 2a,b) would be the most suitable explanation
PDF
Album
Supp Info
Full Research Paper
Published 04 Jun 2025

Origami with small molecules: exploiting the C–F bond as a conformational tool

  • Patrick Ryan,
  • Ramsha Iftikhar and
  • Luke Hunter

Beilstein J. Org. Chem. 2025, 21, 680–716, doi:10.3762/bjoc.21.54

Graphical Abstract
  • via multiple fluorines is seen with the trifluorinated cyclohexene 34: this molecule prefers the half-chair conformation in which σC–H → σ*C–F hyperconjugation with the flanking methylene groups is maximised (Figure 5) [50]. When discussing small-ring cycloalkanes, it is impossible to ignore a
PDF
Album
Review
Published 02 Apr 2025

The effect of neighbouring group participation and possible long range remote group participation in O-glycosylation

  • Rituparna Das and
  • Balaram Mukhopadhyay

Beilstein J. Org. Chem. 2025, 21, 369–406, doi:10.3762/bjoc.21.27

Graphical Abstract
PDF
Album
Review
Published 17 Feb 2025

Synthesis of novel fluorinated building blocks via halofluorination and related reactions

  • Attila Márió Remete,
  • Tamás T. Novák,
  • Melinda Nonn,
  • Matti Haukka,
  • Ferenc Fülöp and
  • Loránd Kiss

Beilstein J. Org. Chem. 2020, 16, 2562–2575, doi:10.3762/bjoc.16.208

Graphical Abstract
  • NOESY was unsuccessful. The reason is that cyclohexenes have a half-chair conformation, and the hydrogen atoms to undergo important NOESY interactions are simply too far away from each other. To solve this problem, the olefin bond of (rac)-35 was hydrogenated to a cyclohexane, affording the fluorinated
PDF
Album
Supp Info
Full Research Paper
Published 16 Oct 2020

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

  • Yana I. Sakhno,
  • Maryna V. Murlykina,
  • Oleksandr I. Zbruyev,
  • Anton V. Kozyryev,
  • Svetlana V. Shishkina,
  • Dmytro Sysoiev,
  • Vladimir I. Musatov,
  • Sergey M. Desenko and
  • Valentyn A. Chebanov

Beilstein J. Org. Chem. 2020, 16, 281–289, doi:10.3762/bjoc.16.27

Graphical Abstract
  • the structure as ethyl 5-(4-bromophenyl)-3-cyano-7-((4-cyano-1H-pyrazol-5-yl)amino)-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-7-carboxylate (Figure 2). Compound 4g existed as a solvate with acetonitrile in the crystal lattice. The tetrahydropyrimidine ring adopted a half-chair conformation (the
PDF
Album
Supp Info
Full Research Paper
Published 27 Feb 2020

Photochromic diarylethene ligands featuring 2-(imidazol-2-yl)pyridine coordination site and their iron(II) complexes

  • Andrey G. Lvov,
  • Max Mörtel,
  • Anton V. Yadykov,
  • Frank W. Heinemann,
  • Valerii Z. Shirinian and
  • Marat M. Khusniyarov

Beilstein J. Org. Chem. 2019, 15, 2428–2437, doi:10.3762/bjoc.15.235

Graphical Abstract
  • that bond. Two iron(II) centers are 8.057 Å apart in the dimer. The ligand 6 appears in the open-ring form and the parallel conformation [8], with the α-methyl groups pointing in similar directions. While still appearing in a distorted half-chair conformation, the phenyl substituent of the
PDF
Album
Supp Info
Letter
Published 15 Oct 2019

An anomalous addition of chlorosulfonyl isocyanate to a carbonyl group: the synthesis of ((3aS,7aR,E)-2-ethyl-3-oxo-2,3,3a,4,7,7a-hexahydro-1H-isoindol-1-ylidene)sulfamoyl chloride

  • Aytekin Köse,
  • Aslı Ünal,
  • Ertan Şahin,
  • Uğur Bozkaya and
  • Yunus Kara

Beilstein J. Org. Chem. 2019, 15, 931–936, doi:10.3762/bjoc.15.89

Graphical Abstract
  • , the cyclohexene ring has a twist-boat conformation and the pyrrolidine rings are in half-chair conformation. The structures contain four asymmetric carbon atoms and the stereogenic centers are as follows: C1(R), C6(S), C11(R), and C16(S), where the N-chlorosulfonyl group attached to the carbonyl atom
PDF
Album
Supp Info
Letter
Published 16 Apr 2019

6’-Fluoro[4.3.0]bicyclo nucleic acid: synthesis, biophysical properties and molecular dynamics simulations

  • Sibylle Frei,
  • Andrei Istrate and
  • Christian J. Leumann

Beilstein J. Org. Chem. 2018, 14, 3088–3097, doi:10.3762/bjoc.14.288

Graphical Abstract
  • orientation and the six-membered ring in a twist-boat conformation (Figure 3b). Approximately 1 kJ/mol higher in energy was the second conformer where the furanose unit adopted a C3’-exo arrangement and the cyclohexene unit a half-chair conformation (Figure 3c). The C(5’) hydroxy group adopted in both
PDF
Album
Supp Info
Full Research Paper
Published 20 Dec 2018

The simple production of nonsymmetric quaterpyridines through Kröhnke pyridine synthesis

  • Isabelle Sasaki,
  • Jean-Claude Daran and
  • Gérard Commenges

Beilstein J. Org. Chem. 2015, 11, 1781–1785, doi:10.3762/bjoc.11.193

Graphical Abstract
  • -chair conformation. The packing is stabilised by van der Waals contacts and weak π–π interactions between symmetry related N2-C21-C22-C23-C24-C25 and N4-C41-C42-C43-C44-C45 pyridine rings (1+x, y, z) with a centroid-to-centroid distance of 3.761(2) Å, and an average interatomic distance between planes
  • deviation being −0.052(2) at C134. These two planes make a dihedral angle of 20.48(5)°. The carbon atoms C133 and C135 of the pinene fragment are roughly symmetrically distributed above and below the N1-C11-C12-C13-C14-C15-C131-C132-C134 planes by −1.118(3) and 1.008(3). Thus, both the C6 rings adopt a half
PDF
Album
Supp Info
Letter
Published 30 Sep 2015

Synthesis and characterization of the cyanobenzene-ethylenedithio-TTF donor

  • Sandrina Oliveira,
  • Dulce Belo,
  • Isabel C. Santos,
  • Sandra Rabaça and
  • Manuel Almeida

Beilstein J. Org. Chem. 2015, 11, 951–956, doi:10.3762/bjoc.11.106

Graphical Abstract
  • one crystallographically independent molecule in a general position (Figure 1). This molecule is almost planar; the dihydrodithiin ring adopts a half-chair conformation with five coplanar atoms. The central C=C bond length (C5–C6 = 1.355(8) Å) is typical of neutral TTF donors [17][18][19][20]. The
PDF
Album
Supp Info
Letter
Published 03 Jun 2015

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

Graphical Abstract
  • [3 + 2] cycloadditions, we believe that in the TS the respective nitronates present a half-chair conformation with the HC(4) substituent and the alkoxy group in an axial position to maximize the stabilization generated by the anomeric effect [9][33][41][42]. Thus, the competitive endo/exo approach of
PDF
Album
Supp Info
Full Research Paper
Published 30 Apr 2013

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

  • Marcin Jasiński,
  • Dieter Lentz and
  • Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

Graphical Abstract
  • solution to give crystals suitable for an X-ray crystallographic analysis (Figure 2). The X-ray analysis of (3R)-3a shows a well-defined half-chair conformation of the 1,2-oxazine ring, with four carbon atoms in plane and with ONCC and OCCC torsion angles of −60° and 13°, respectively. The bulky N
  • from the moderate hindrance exhibited by the neighbouring phenyl substituent, which in the case of the (3S)-series probably occupies a pseudo-equatorial position in the half-chair conformation of the 3,6-dihydro-2H-1,2-oxazine derivatives 3. The higher stereoselectivity of the hydroboration of (3R)-3a
PDF
Album
Supp Info
Full Research Paper
Published 30 Apr 2012

Intramolecular carbenoid ylide forming reactions of 2-diazo-3-keto-4-phthalimidocarboxylic esters derived from methionine and cysteine

  • Marc Enßle,
  • Stefan Buck,
  • Roland Werz and
  • Gerhard Maas

Beilstein J. Org. Chem. 2012, 8, 433–440, doi:10.3762/bjoc.8.49

Graphical Abstract
  • two diastereomers. For the six-ring ylide 12a (isomer ratio A:B = 4:1) a stereochemical assignment was made based on 1H NMR studies (Figure 1 and Table 1). We propose that the major isomer 12aA assumes a cyclohexene-like half-chair conformation, and the minor isomer 12aB, which has the opposite
PDF
Album
Supp Info
Full Research Paper
Published 22 Mar 2012

Amine-linked diglycosides: Synthesis facilitated by the enhanced reactivity of allylic electrophiles, and glycosidase inhibition assays

  • Ian Cumpstey,
  • Jens Frigell,
  • Elias Pershagen,
  • Tashfeen Akhtar,
  • Elena Moreno-Clavijo,
  • Inmaculada Robina,
  • Dominic S. Alonzi and
  • Terry D. Butters

Beilstein J. Org. Chem. 2011, 7, 1115–1123, doi:10.3762/bjoc.7.128

Graphical Abstract
  • coupling constant (9.8 Hz), which can only be explained by a trans relationship of the 4-H and 5-H protons and a OH5 half-chair conformation. The J4,5 coupling constants for the products assigned as threo were not always well resolved, but in 12, a smaller coupling constant (ca. 4 Hz) was seen. Having
PDF
Album
Supp Info
Full Research Paper
Published 16 Aug 2011

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

Graphical Abstract
  • reversibility requires an antiperiplanar relationship between the nucleophile and the epoxide oxygen in the product immediately after reaction. From a given half-chair conformation of the epoxide, nucleophilic attack results in either a chair (with the substituents trans-diaxial) or a skew-boat conformation
PDF
Album
Supp Info
Full Research Paper
Published 29 Nov 2010

Trifluoromethyl ethers – synthesis and properties of an unusual substituent

  • Frédéric R. Leroux,
  • Baptiste Manteau,
  • Jean-Pierre Vors and
  • Sergiy Pazenok

Beilstein J. Org. Chem. 2008, 4, No. 13, doi:10.3762/bjoc.4.13

Graphical Abstract
  • -1,4-benzodioxine (7, Figure 3) which occupies a half-chair conformation, shows clearly differences between quasi-axial and quasi-equatorial fluorine atoms. The average bond lengths of 1.355 and 1.330 Å differ significantly [48]. The effect of replacing a methyl by a trifluoromethyl moiety on bond
PDF
Album
Review
Published 29 Apr 2008
Other Beilstein-Institut Open Science Activities