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Search for "six-membered ring" in Full Text gives 137 result(s) in Beilstein Journal of Organic Chemistry.

Structures of the reaction products of the AZADO radical with TCNQF4 or thiourea

  • Hideto Suzuki,
  • Yuta Kawahara,
  • Hiroki Akutsu,
  • Jun-ichi Yamada and
  • Shin’ichi Nakatsuji

Beilstein J. Org. Chem. 2013, 9, 1487–1491, doi:10.3762/bjoc.9.169

Graphical Abstract
  • AZADO molecule in the next step to give an addition product (a salt) resulting from the addition to one of the double bonds in the six-membered ring. Finally, the oxoammonium cation in the adduct will react with the counter anion from the less hindered site to afford the final product 5 with trans
  • -membered ring in a trans-manner, as seen from its molecular structure (Scheme 1) (Figure 2). Therefore, a plausible mechanism of the reaction could be considered as shown in Scheme 2. First, a transient CT complex would be formed between 2 and 3 but it would be unstable enough to be attacked by another
  • amount of TCNQF4 (3) did not give dark blue crystals but gave an orange solid. After purification, the orange crystals obtained were proved to be the addition product 5 and not a CT complex as seen from the X-ray analysis. Furthermore, the addition was found to take place to a double bond of the six
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Published 25 Jul 2013

Anionic cascade reactions. One-pot assembly of (Z)-chloro-exo-methylenetetrahydrofurans from β-hydroxyketones

  • István E. Markó and
  • Florian T. Schevenels

Beilstein J. Org. Chem. 2013, 9, 1319–1325, doi:10.3762/bjoc.9.148

Graphical Abstract
  • -methyleneketals [1][2][3]. This unique transformation is particularly efficient in the case of six-membered ring ketones (Scheme 1). In an attempt to extend the scope of this cascade process to acyclic ketones, acetone was submitted to the usual reaction conditions. To our surprise, the expected adduct 5 was
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Published 03 Jul 2013

Host–guest complexes of mixed glycol-bipyridine cryptands: prediction of ion selectivity by quantum chemical calculations, part V

  • Svetlana Begel,
  • Ralph Puchta and
  • Rudi van Eldik

Beilstein J. Org. Chem. 2013, 9, 1252–1268, doi:10.3762/bjoc.9.142

Graphical Abstract
  • ) building block causes a stronger contraction of the cryptand hole, since the two pyridine rings are stiffened by a third, weaker aromatic six-membered ring (according to Clar’s rule [72][73][74]) as was explained above. Hence, the subsequent substitution by (bpy) and (phen) moieties reduces the size of the
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Published 27 Jun 2013

Conformational analysis and intramolecular interactions in monosubstituted phenylboranes and phenylboronic acids

  • Josué M. Silla,
  • Rodrigo A. Cormanich,
  • Roberto Rittner and
  • Matheus P. Freitas

Beilstein J. Org. Chem. 2013, 9, 1127–1134, doi:10.3762/bjoc.9.125

Graphical Abstract
  • constant. Better electron donors than fluorine (N, P and S) perform such an interaction. An intramolecular hydrogen bond F∙∙∙HO appears in 2-fluorophenylboronic acid and it contributes for the conformational stability, since a six-membered ring is formed from this interaction, which is more efficient than
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Published 11 Jun 2013

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
  • resulting from the endo approach of the smaller dipolarophile MVK by the Re face of the nitronate. It is worthwhile to mention that, depending of the nitroso acetal structure, an opening of the six-membered ring is caused due to a greater sensitivity to the reaction medium, leading to generation of the
  • could be corroborated by X-ray analysis of 11b, since the diastereoselection of the [4 + 2]-step was the same for all cycloadditions investigated (Figure 1 and Figure 2). The determination of the vicinal H,H constant coupling of the protons located in the six-membered ring was not so simple due to the
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Published 30 Apr 2013

Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

  • Holger F. Bettinger and
  • Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

Graphical Abstract
  • unstable with respect to dimerisation or oligomerisation. In 1,2-dihydro-1,2-azaborine, such a dimerisation is not observed, probably due to the aromatic character of the six-membered ring. In 3, however, this aromatic stabilisation is no longer available. For the sake of simplicity, we only considered
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Published 18 Apr 2013

A new intermediate in the Prins reaction

  • Shinichi Yamabe,
  • Takeshi Fukuda and
  • Shoko Yamazaki

Beilstein J. Org. Chem. 2013, 9, 476–485, doi:10.3762/bjoc.9.51

Graphical Abstract
  • was used, and water or glacial acetic acid was the solvent. A general Prins reaction is shown in Scheme 1. A typical Prins reaction is exhibited in Scheme 2 [4]. Here, the six-membered ring compound, 4,4-dimethyl-1,3-dioxane, is the major product along with 3-methyl-1,3-butane-diol. The 1,3-dioxane is
  • the carbonyl group. In this case, 1,3-diol(Me) is the alcohol, and the second formaldehyde is of the C=O group. Closure of the six-membered ring from the ether(Me) [TS4(Me)] gives the product 4-methyl-1,3-dioxane, dioxane(Me). Thus, the obtained route (ii), precursor (Me) → diol(Me) → ether(Me
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Published 05 Mar 2013

Polymerization of novel methacrylated anthraquinone dyes

  • Christian Dollendorf,
  • Susanne Katharina Kreth,
  • Soo Whan Choi and
  • Helmut Ritter

Beilstein J. Org. Chem. 2013, 9, 453–459, doi:10.3762/bjoc.9.48

Graphical Abstract
  • be assumed that the driving force for the ring closure is the formation of a six-membered ring; however, the mechanism has not been investigated in detail so far. Since the ring closure does not affect the spectral properties, 14 can still be used as a polymerizable red dye. In this work, side
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Published 28 Feb 2013

Design and synthesis of quasi-diastereomeric molecules with unchanging central, regenerating axial and switchable helical chirality via cleavage and formation of Ni(II)–O and Ni(II)–N coordination bonds

  • Vadim A. Soloshonok,
  • José Luis Aceña,
  • Hisanori Ueki and
  • Jianlin Han

Beilstein J. Org. Chem. 2012, 8, 1920–1928, doi:10.3762/bjoc.8.223

Graphical Abstract
  • diastereomeric complexes (Ra*,Ph*,Sc*)-2 and (Ra*,Mh*,Rc*)-3, which contain at least three elements of chirality, namely stereogenic center, axis and helix (Scheme 1). The structure of these complexes incorporated two five- and one six-membered ring displaying a square-planar geometry. It is worth mentioning
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Published 13 Nov 2012

Determination of the relative configuration of tropinone and granatanone aldols by using TBDMS ethers

  • Ryszard Lazny,
  • Aneta Nodzewska,
  • Katarzyna Sidorowicz and
  • Przemyslaw Kalicki

Beilstein J. Org. Chem. 2012, 8, 1877–1883, doi:10.3762/bjoc.8.216

Graphical Abstract
  • (Figure 3) by X-ray diffraction. Atoms H1 and H8 were found in syn relation to each other, while the 1′-hydroxybenzyl group at C1 is on the exo side of the bicyclic tropane scaffold pointing towards the C4–N1–C7 bridge (pseudoaxial on the tropinone six-membered ring). The crystal structure is also
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Published 02 Nov 2012

Evaluation of a chiral cubane-based Schiff base ligand in asymmetric catalysis reactions

  • Kyle F. Biegasiewicz,
  • Michelle L. Ingalsbe,
  • Jeffrey D. St. Denis,
  • James L. Gleason,
  • Junming Ho,
  • Michelle L. Coote,
  • G. Paul Savage and
  • Ronny Priefer

Beilstein J. Org. Chem. 2012, 8, 1814–1818, doi:10.3762/bjoc.8.207

Graphical Abstract
  • cyclopropanation and Michael addition reactions. Although there was no increase in stereocontrol, upon computational evaluation using both M06L and B3LYP calculations, it was revealed that a pseudo six-membered ring exists, through H-bonding of a cubyl hydrogen to the copper core. This decreases the steric bulk
  • complex. In addition, H-bonding with cubyl hydrogens and the copper core yielded a pseudo six-membered ring, which decreased the N–C–C–N dihedral angle. Structure of (1R,2R)-N,N’-bis[(4-iodocuban-1-yl)methylene]-trans-1,2-diamino cyclohexane (1). M06L DFT global minima for (a) (1R,2R)-N,N’-bis[(4
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Published 22 Oct 2012

Imidazolinium and amidinium salts as Lewis acid organocatalysts

  • Oksana Sereda,
  • Nicole Clemens,
  • Tatjana Heckel and
  • René Wilhelm

Beilstein J. Org. Chem. 2012, 8, 1798–1803, doi:10.3762/bjoc.8.205

Graphical Abstract
  • geometry of 7-membered 1,3-diazepinium cations such as 19 does not allow the planar conformation to be kept, thus the positive charge is less delocalized over the NCN atoms (Scheme 4) [26][27][28][29]. Salt 16, incorporating a six-membered ring as the smallest ring, displayed a catalytic activity between
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Published 18 Oct 2012

Cation affinity numbers of Lewis bases

  • Christoph Lindner,
  • Raman Tandon,
  • Boris Maryasin,
  • Evgeny Larionov and
  • Hendrik Zipse

Beilstein J. Org. Chem. 2012, 8, 1406–1442, doi:10.3762/bjoc.8.163

Graphical Abstract
  • -membered ring to bicyclic 3,4-diaminopyridines leads to tricyclic diaminopyridines 407, 408, and 410 and is accompanied by an increase in acetyl cation affinities above 240 kJ/mol. Annelation of a carbocyclic ring thus has a comparabel effect as already observed for DMAP (54) and its ring-extended forms
  • respective ACA values (Table 14). Most of the 3,4-diaminopyridines (58, 59, 63, 399–408) show ACA values which are roughly between 235 and 243 kJ/mol. However, the introduction of a (thio)urea moiety as in 383–387, 389–394, and 397 lowers the ACA value by 10 to 25 kJ/mol. Annelation of an additional six
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Published 31 Aug 2012

Binaphthyl-anchored antibacterial tripeptide derivatives with hydrophobic C-terminal amino acid variations

  • John B. Bremner,
  • Paul A. Keller,
  • Stephen G. Pyne,
  • Mark J. Robertson,
  • K. Sakthivel,
  • Kittiya Somphol,
  • Dean Baylis,
  • Jonathan A. Coates,
  • John Deadman,
  • Dharshini Jeevarajah and
  • David I. Rhodes

Beilstein J. Org. Chem. 2012, 8, 1265–1270, doi:10.3762/bjoc.8.142

Graphical Abstract
  • hydrophobicity while increasing the hydrophilicity of the six-membered ring in 2c through inclusion of a ring oxygen atom, as in 2d, had a significant detrimental effect on the activity against the vancomycin-resistant strains VRE449 and VRE820. Interestingly, the placement of an extra methylene group in the
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Published 09 Aug 2012

Conformational analysis, stereoelectronic interactions and NMR properties of 2-fluorobicyclo[2.2.1]heptan-7-ols

  • Fátima M. P. de Rezende,
  • Marilua A. Moreira,
  • Rodrigo A. Cormanich and
  • Matheus P. Freitas

Beilstein J. Org. Chem. 2012, 8, 1227–1232, doi:10.3762/bjoc.8.137

Graphical Abstract
  • perform well in estimating 19F-based couplings [23]), and a high correlation was found (R2 = 0.97), indicating that such an interaction, and thus the F∙∙∙HO intramolecular HB forming a six-membered ring, modulates the 1hJF,H(O) SSCC (Figure 4), which is governed by the Fermi contact term. The SSCC
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Published 02 Aug 2012

Synthesis of 2,6-disubstituted tetrahydroazulene derivatives

  • Zakir Hussain,
  • Henning Hopf,
  • Khurshid Ayub and
  • S. Holger Eichhorn

Beilstein J. Org. Chem. 2012, 8, 693–698, doi:10.3762/bjoc.8.77

Graphical Abstract
  • , which was recrystallized from hexane and dichloromethane to afford single crystals suitable for X-ray analysis. The X-ray data [20] showed that the central, six-membered ring is almost planar but is slightly folded about the axis C(2)···C(6); the five-membered ring is essentially planar. The two larger
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Published 04 May 2012

Photochemical and thermal intramolecular 1,3-dipolar cycloaddition reactions of new o-stilbene-methylene-3-sydnones and their synthesis

  • Kristina Butković,
  • Željko Marinić,
  • Krešimir Molčanov,
  • Biserka Kojić-Prodić and
  • Marija Šindler-Kulyk

Beilstein J. Org. Chem. 2011, 7, 1663–1670, doi:10.3762/bjoc.7.196

Graphical Abstract
  • protons A and B with an aromatic proton (H-2) at 7.00 ppm is seen, as well as the interaction of proton C with protons E and D. Since the NOE interaction is seen between protons A and E we concluded that protons A and E must lie on the same side of the six-membered ring. In addition, the interaction of
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Published 13 Dec 2011

Intramolecular hydroamination of alkynic sulfonamides catalyzed by a gold–triethynylphosphine complex: Construction of azepine frameworks by 7-exo-dig cyclization

  • Hideto Ito,
  • Tomoya Harada,
  • Hirohisa Ohmiya and
  • Masaya Sawamura

Beilstein J. Org. Chem. 2011, 7, 951–959, doi:10.3762/bjoc.7.106

Graphical Abstract
  • participated in the cyclization to form azabicylo[5.4.0]decene 5o in 76% yield along with a small amount of exomethylene isomer 6o (5o/6o 98:2, Table 4, entry 4). Effect of ring sizes We also evaluated the triethynylphosphine L1, X-Phos, and IPr for an acceleration effect in the six-membered, ring forming
  • , gold-catalyzed hydroamination of N-(5-hexyn-1-yl)-p-toluenesulfonamide 7. As expected from entropy considerations, the six-membered ring formations of 7 with these ligands were generally much faster than the seven-membered ring formations of 4: The reaction with 0.5 mol % catalyst loading at room
  • temperature completed within 1 h irrespective of the ligand used. When the catalyst loading was reduced to 0.1 mol %, however, the superiority of L1 to X-Phos and IPr became significant, as shown in Table 5. The reaction with L1 at room temperature afforded the six-membered ring product 8 in 91% isolated
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Published 08 Jul 2011

Recent advances in the gold-catalyzed additions to C–C multiple bonds

  • He Huang,
  • Yu Zhou and
  • Hong Liu

Beilstein J. Org. Chem. 2011, 7, 897–936, doi:10.3762/bjoc.7.103

Graphical Abstract
  • gold-catalyzed rearrangement of 6-alkynylbicyclo[3.1.0]hexen-2-enes 209 has been developed [93]. In this reaction, divergent structural rearrangements are observed in the absence/presence of nucleophiles. The process results in a novel five-to-six-membered ring expansion that involves cleavage of the
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Published 04 Jul 2011

Synthetic applications of gold-catalyzed ring expansions

  • David Garayalde and
  • Cristina Nevado

Beilstein J. Org. Chem. 2011, 7, 767–780, doi:10.3762/bjoc.7.87

Graphical Abstract
  • aziridines onto the adjacent alkyne afforded the 2,5-disubstituted pyrroles 52 in high yields (Scheme 16). In 2011, Barluenga et al. developed a new methodology for the preparation of 1,6-disubstituted regioisomeric cyclohexadienes 54 and 54' (Scheme 17) [46]. The process resulted in a five-to-six-membered
  • ring expansion which involves the cleavage of the bridging C–C bond and a formal [1,2]-alkynyl shift. A mixture of regioisomers resulted due to an unexpected equilibration of the starting material 53 to 53' via 6-endo cyclization of the olefin with the gold-activated alkyne. 3 Ring expansions of
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Published 07 Jun 2011

Gold-catalyzed heterocyclizations in alkynyl- and allenyl-β-lactams

  • Benito Alcaide and
  • Pedro Almendros

Beilstein J. Org. Chem. 2011, 7, 622–630, doi:10.3762/bjoc.7.73

Graphical Abstract
  • exclusively β-lactam–tetrahydrofuran hybrids 6 in good isolated yields (Scheme 3). Besides total chemocontrol, the reaction was regiospecific and only the five-membered ring ether was formed: The isomeric six-membered ring product was not observed. By contrast, when the cyclization of olefinic α-allenols 5
  • medium-sized rings also reacted well to yield interesting seven- or eight-membered ring fused dihydroindolizinones in good yields. Surprisingly, the corresponding cyclopentene or cyclohexene substrates did not afford the corresponding five- or six-membered ring-fused dihydroindolizinones. After 10 h, the
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Published 17 May 2011

A gold-catalyzed alkyne-diol cycloisomerization for the synthesis of oxygenated 5,5-spiroketals

  • Sami F. Tlais and
  • Gregory B. Dudley

Beilstein J. Org. Chem. 2011, 7, 570–577, doi:10.3762/bjoc.7.66

Graphical Abstract
  • having been made on systems that include at least one six-membered ring [5]. 5,5-Spiroketals (m, n = 0, Figure 1), particularly oxygenated 5,5-spiroketals such as are found in the cephalosporolides (Figure 2), are the focus of this study. A variety of synthetic methods are available for the synthesis of
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Published 04 May 2011

Palladium-catalyzed formation of oxazolidinones from biscarbamates: a mechanistic study

  • Benan Kilbas and
  • Metin Balci

Beilstein J. Org. Chem. 2011, 7, 246–253, doi:10.3762/bjoc.7.33

Graphical Abstract
  • cyclopropyl hydrogens H-6 in 8 and 16 are located over the six-membered ring. These hydrogen atoms block the syn-face of the double bond and may hinder the approach of the palladium complex from the side of the cyclopropane ring. However, the products 9 and 17 were formed under the same reaction conditions in
  • 58 and 51% yield, respectively. If the proposed mechanism (Scheme 6) is correct, then the hydrogen atoms (H-6) in 8 and 16 cannot generate a steric hindrance to prevent the reaction. In order to increase the bulkiness of the substituents located over the six-membered ring, the hydrogen atom was
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Published 24 Feb 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
  • could offer a route to α-configured galactofuranoside pseudodisaccharides via a subsequent epimerisation of the unprotected C2 alcohol, analogous to the α-manno to α-gluco epimerisation route developed by Ogawa in the six-membered ring series [17]. In this paper we report our results on the synthesis of
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Published 29 Nov 2010

β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

  • Jaya S. Kudavalli and
  • Rory A. More O'Ferrall

Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118

Graphical Abstract
  • by a factor of 18. However, in this case, participation of oxygen as a neighbouring group is well established [15]. Participation by oxygen in a six-membered ring is excluded for solvolysis of endo (although not exo) norbornyl brosylate substituted with oxygen at the 4-position (12). Comparison with
  • the carbocyclic substrate in this case shows a rate retardation of 80,000 [16]. This value has been considered exceptionally large and an additional rate-retarding effect has been attributed to ring strain induced by the presence of oxygen in the six-membered ring of the bicyclic carbocation
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Published 03 Nov 2010
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