Journal of the Chemical Society Perkin Transactions 2 (Perkin Trans 2 )

Publisher: Chemical Society (Great Britain); Royal Society of Chemistry (Great Britain)

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  • Website
    Perkin Transactions 2 website
  • Other titles
    Journal of the Chemical Society. Perkin transactions. II, Journal of the Chemical Society., JCS Perkin 2, Journal of the Chemical Society., Perkin transactions II, Perkin transactions., Physical organic chemistry, J.C.S. Perkin 2, Perkin transactions 2
  • ISSN
    1472-779X
  • OCLC
    1064266
  • Material type
    Periodical, Internet resource
  • Document type
    Journal / Magazine / Newspaper, Internet Resource

Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: The rate constants for the dihydroxylation of (E)-ethyl cinnamate with osmium tetroxide in toluene were determined at atmospheric and high pressure indicating a slight acceleration by high-pressure. The volume of activation was determined to be –12 ± 2 cm3 mol–1 for this transformation. This relatively small negative value can not be explained with a simple [3 + 2]-mechanism for which a significantly more negative value should be expected.
    Journal of the Chemical Society Perkin Transactions 2 06/2013;
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    ABSTRACT: The novel N-aryl-4-chloro-3-methyl-2(1H)-quinolones (1)–(4) have been synthesized by condensation of the appropriate diphenylamine with diethyl methylmalonate and subsequent chlorination of the resulting N-aryl-4-hydroxy-3-methyl-2(1H)-quinolones (7)–(10). 5-(1-Naphthyl)-6(5H)-phenanthridinone (5) has been synthesized by the Chapman rearrangement of the 6-(1 -naphthoxy)phenanthridine (11). Separation of the enantiomers (M) and (P) of the quinolones (1)–(4) and phenanthridinones (5), (6) was achieved by liquid chromatography on triacetylcellulose. The barriers to partial rotation about the C–N bond in (1)–(6) were determined by thermal racemization of enantiomers and are compared with those of structurally related molecules.
    Journal of the Chemical Society Perkin Transactions 2 05/2013; 1:619-624.
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    ABSTRACT: HeI photoelectron (PE) spectra of 13 N-aryl- and N-heteroaryl-pyrroles have been measured. The low energy region of the spectra has been analysed using semiempirical MNDO SCF MO calculations [assuming the validity of Koopmans’ theorem (Physica, 1934, 1, 104)] and the composite molecule method (CMM) which has proven to be particularly useful for electronic structure elucidation of complex molecules. Electronic structure, especially in terms of the distribution of the outer valence electrons over the molecule, has been shown previously to be mostly responsible for their chemical properties.
    Journal of the Chemical Society Perkin Transactions 2 05/2013; 12:2597-2604.
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    ABSTRACT: The regioselective protection of secondary hydroxy groups of gluco-, galacto-, manno-, rhamno- and fucopyranosides using TBDPSCl with imidazole in DMF has been studied. It was found that the relative spatial arrangement of the OH groups modulates the silylation selectivity which arises from the combination of kinetic factors and the intramolecular migrations of the secondary TBDPS groups. The rearrangement of the TBDPS groups has a much larger effect on the α-D-manno- and α-L-rhamnopyranosides, allowing the protection of the OH groups at positions 2, 3 or 2 and 4, in synthetically useful yields, by changing the reaction conditions. The relative reactivity of the secondary OH groups seems particularly likely to be governed by steric factors. This trend provides a valuable approach to the synthesis of 3-O-tert-butyldiphenylsilyl-1-thio-β-L-fucopyranoside.
    Journal of the Chemical Society Perkin Transactions 2 08/2002;
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    ABSTRACT: N-(2-Aminoacetyl)-ε-caprolactam (1) was synthesized. When 1 is dissolved in aprotic solvents such as chloroform or dichloromethane and water (D2O), a ca. 1 ∶ 1 equilibrium is established between two isomeric forms: cyclol1c and macrocyclic diamide1d. The methylene protons –NHCH2CON– for both forms become diastereotopic. Therefore, the diastereotopic interconversion of 1c and 1d can be followed by dynamic 1H-NMR. In D2O, specific base catalysis is observed for both interconversions. Since the equilibrium K = kobs.f/kobs.r for the 1c = 1d transformation remains the same over the wide pD range studied (2 < pD < 11), a mechanism is proposed whereby the exchange occurs through the cyclol1c conjugate base. According to this mechanism, kobs.f and kobs.r can be measured by the diastereotopic interconversions of 1c and 1d respectively. Therefore, K = kobs.f/kobs.r = k2[H2O]Ka/k−2Kw, where k2 is the rate of cleavage of the cyclol 1c (of acidity constant Ka) conjugate base toward the macrocyclic diamide, and k−2 represents the reverse amino amide-to-carbonyl amide attack (transannular cyclolization). Values for k2 of 1.8 × 102 M−1 s−1 (ΔG‡ = 59.8 kJ mol−1 at 25 °C), and k−2 of 1 × 105 M−1 s−1 (ΔG‡ = 44.3 kJ mol−1 at 25 °C) were obtained. The uncatalyzed rates of kobs.f = ko1c and kobs.r = ko1d were also measured. These values are 2 s−1 (ΔG‡ = 71.1 kJ mol−1 at 25 °C) and 4 s−1 (ΔG‡ = 69.4 kJ mol−1 at 25 °C), respectively.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: The single crystal X-ray structure of a homodimer of a tetra(tolylurea) calix[4]arene including a tetraethylammonium cation as guest shows an expansion of the capsule and a distortion of its shape, in comparison to the structure of a similar dimer with an encapsulated benzene molecule. Thus, only 8 of 16 possible hydrogen bonds are present in the hydrogen bonded belt holding together the two hemispheres. The encapsulated cation is disordered over two equivalent positions with two methyl groups pointing to the equator, while two methyl groups pointing to the poles form CH–π interactions with the inner surfaces of the calixarene cavities. MD simulations are in agreement with the distorted X-ray structure for a short simulation time of 1–2 ns with a given orientation of the included cation and approach for longer simulation times (9 ns) the fourfold symmetry found by 1H NMR spectroscopy in solution.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: Stereoselective rearrangements of e.g. meso-epoxides by chiral lithium amides yield chiral allylic alcs. in high enantiomeric excess. Such products are useful synthetic intermediates. Lithium (S)-2-(pyrrolidin-1-ylmethyl)pyrrolidide Li-2 has been found to deprotonate cyclohexene oxide 1 in THF (THF) to yield the allylic lithium alkoxide of (S)-cyclohex-2-en-1-ol (S)-Li-3 in 80% ee. Upon changing solvent from THF to 2,5-dimethyltetrahydrofuran (2,5-DMTHF) a 1,3-proton transfer of (S)-Li-3 is induced yielding the lithium alkoxide of (S)-cyclohex-3-en-1-ol (S)-Li-4. Thus the reaction gives access to the homoallylic alc. 4. This rearrangement has previously been shown to take place with retention of the stereocenter and intramolecularly. We here report further results on the stereochem. of this isomerization. For this purpose a synthesis of the deuterium labeled compd., (S)-2-deuterio-3-methylcyclohex-2-en-1-ol (S)-2H-5, has been developed. Solvent induced isomerization of the lithium alkoxide of (
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: We have synthesized compounds: N-(2-aminoacetyl)-2-pyrrolidone (1) and N-(2-aminoacetyl)-2-piperidone (2). When these compounds are dissolved in aprotic or protic solvents a fast equilibrium ca. 1:1 between the cyclol form (tetrahedral intermediate) and the bislactam macrocycle is established. The same result has been reported previously for N-(2-aminoacetyl)-2-caprolactam (3). For compounds 2 and 3, dynamic 1H-NMR (using the methylene signals α to the carbonyl and to the amino group) through spectrum simulation has been used to evaluate the exchange between the two mentioned forms at different pH. However, for compound 1 the exchange was evaluated using magnetization transfer technique. The more stable bislactam configuration of the macrocycle form in compounds 2 and 3, is the trans–cis (one lactam with the cyclic alkyl chains trans oriented and the other cis oriented). However, the same form for compound 1 has a more stable cis–cis bislactam configuration. This difference in configuration induces substantial changes in the appearance of the methylene 1H-NMR signals that precludes the use of line-shape analysis to evaluate the rates. The rate law for the proposed mechanism of exchange between the cyclol form and the macrocycle is: K = [macrocycle]/[cyclol] = kobs.f/kobs.r = Kak2[H2O]/[H+]/k−2Kw/[H+] = Kak2[H2O]/k−2Kw; where Ka is the acidity equilibrium constant of the cyclol form, Kw = 10−14 M2 and k2 and k−2 are the second order rate constants for the specific exchange catalysis. Therefore, both, the macrocycle formation (kobs.f) and the cyclol formation (kobs.r) are specific base catalyzed; however the equilibrium constant is independent of pH. Since K is ca. 1, the ΔG≠ associated with the measured rate constants represent the intrinsic barrier for this non-identical thermoneutral transformation where a cleavage of a tetrahedral intermediate is involved. The activation energies associated with the reverse rate constants then correspond to the intrinsic barrier for transannular cyclolization.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: The reaction between 4,6-dimethyl-1,2,3-triazine and cyclopentanone pyrrolidine enamine has been studied using ab initio SCF-MO computational methods. Solvent effects have also been taken into account. The reaction is predicted to be a concerted Diels–Alder cycloaddition. Self-consistent reaction field methods based on multipole expansions of the free energy of solvation tend to overestimate the stability of zwitterionic intermediates at the Hartree–Fock level. This overestimation results in a stepwise mechanism, although higher levels of theory predict a concerted mechanism.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: The stereoselectivity of the oxidation of 1,4-thiazane-3,5-dicarboxylate derivatives to the corresponding sulfoxides and sulfones was found to be dependent on the type of oxidant used and the conformational preference of the substrate. Direct oxidants, such as sodium periodate, peroxides and peracids, preferentially react with the axial sulfur lone-pair, providing the axial S-oxide. Oxidation with bromine–water yielded the epimeric equatorial S-oxide, presumably as a result of initial attack of the axial sulfur lone pair providing the axial bromosulfonium ion, with subsequent displacement of bromide by water leading to the equatorial S-oxide.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: Perborate but not percarbonate in acetic acid generates peracetic acid on standing and the peracetic acid oxidation of anilines is fast. The oxidation with a fresh solution of perborate in acetic acid is smooth and second order but the specific oxidation rate increases with increasing [perborate]0 or [boric acid]. Perborate on dissolution affords hydrogen peroxide and a borate; the latter assists the former in the oxidation. The oxidation rates of anilines under identical conditions do not conform to any of the linear free energy relationships but the reaction rates of molecular anilines do. Perborate oxidation proceeds via two reaction paths but the overall oxidation rates of molecular anilines conform to structure–reactivity relationships; the transition states do not differ significantly. Analysis of the oxidation rates of perborate and percarbonate reveals that while perborate oxidation is faster than percarbonate it is at least as selective as the latter.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: Treatment of N-alkoxy-N-chloro- or N-acetoxyamides with sodium azide in aqueous acetonitrile results in SN2 displacement of chlorine or acetate and the formation of reactive N-alkoxy-N-azidoamides which undergo a concerted decomposition to esters and nitrogen. The properties of the model N-azido-N-methoxyformamide have been computed at the B3LYP/6-31G* hybrid density functional level of theory. It is a typical anomeric amide in that the nitrogen is strongly sp3 hybridised resulting in a low amide isomerisation barrier. It decomposes in a two-step process involving exothermic loss of N2 to give 1-formyl-1-methoxydiazene which spontaneously undergoes a HERON decomposition to methyl formate and N2. Overall, the process is highly exothermic (ΔG between −654 and −659 kJ mol−1). The competitive one-step HERON process involving formation of methyl formate and tetrazene is kinetically unfavourable. Sterically hindered ester formation will be facilitated by both exothermicity and a transition state for ester formation which avoids a sterically crowded tetrahedral intermediate.
    Journal of the Chemical Society Perkin Transactions 2 01/2002;
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    ABSTRACT: Complexation studies of eleven N-heteroaromatic cations with tetraphenylborate are reported. Tetraphenylborate forms complexes with five cations and reacts to form Lewis-base boranes with six cations. The complexes and the displacement reaction products were characterised by 1H NMR spectroscopy, elemental analysis and crystallographic methods. In the complexes C–H - π or N–H- π hydrogen bonds are the principal intermolecular interactions. The stability constants for the complexes are determined by 1H NMR titration in acetonitrile–methanol (1 : 1) solution. Crystal structures of four of the complexes and three of the Lewis-base triphenylborane products are reported.
    Journal of the Chemical Society Perkin Transactions 2 12/2001;

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