Complexation of [2.2]paracyclophane with β- and γ-cyclodextrins studied by HPLC and NMR

The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d₇ at room temperature do not show significant complexation, while HPLC of the complexes in mixed H₂O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC, at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H₂O:EtOH exhibits 1:2 stoichiometry with K ₁ = 1×10² ± 2, K ₂ = 9.0×10⁴ ± 2×10³ (K = 9×10⁶) while that with γ-cyclodextrin in 50% H₂O:MeOH exhibits 1:1 stoichiometry with K ₁ = 4×10³ ± 150 M⁻¹. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the β-cyclodextrin complexation at 25°C ΔG ⁰ _CD is −39.7 kJ mol⁻¹ while ΔH ⁰ _CD and ΔS ⁰ _CD are −88.2 kJ mol⁻¹ and −0.16 kJ mol⁻¹ K⁻¹. For γ-cyclodextrin, the corresponding values are ΔG ⁰ _CD = −20.5 kJ mol⁻¹, ΔH ⁰ _CD = −33.5 kJ mol⁻¹ and ΔS ⁰ _CD = −0.04 kJ mol⁻¹ K⁻¹.      

New chiral ligands based on (+)-α-pinene

A number of new chiral ligands were synthesized starting from an accessible monoterpene, (+)-α-pinene. The new ligands were used in the vanadium-catalyzed oxidation of sulfides to chiral sufoxides.     

Synthesis, structure, and biological activity of [2.2]paracyclophanes. 7. Synthesis of 2-([2.2]paracyclophan-4-yl)pyridines,-tetrahydroquinolines, and-benzo[h]quinolines based on condensation of 4-(β-dimethylaminopropionyl)[2.2]paracyclophane with primary amines

Condensation of 4-(-dimethylaminopropionyl)paracyclophane with aliphatic aldehydes or cyclohexanones in the presence of hydroxylamine gave 2-([2.2]paracyclophan-4-yl)pyridines and-5,6,7,8-tetrahydroquinolines respectively. Reaction of these salts with -naphthylamine gives a mixture of paracyclophanyl substituted 1,2,3,4-tetrahydrobeno[h]quinoline and benzo[h]quinoline.For Communication 6, see [1].Russian University of National Friendship, Moscow 117198. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1069–1073, August, 1997.     

Paracyclophanes as model compounds for strongly interacting π-systems. Part 2: mono-hydroxy[2.2]paracyclophane

The structure of the electronic ground- and first excited state of mono-hydroxy [2.2]paracyclophane (MHPC) and the S(1)← S(0) electronic transition have been investigated by resonance-enhanced multiphoton ionisation (REMPI) and by quantum chemical spin-component-scaled-approximate coupled cluster second order (SCS-CC2) computations. The origin of the S(1)← S(0) transition was located at 30,772 cm(-1) (3.815 eV) in the REMPI spectrum. The value has to be compared with a computed excitation energy of 3.79 eV. The vibrational structure of the spectrum confirms a significant geometry change upon excitation along the coordinates corresponding to twist- and shift-motions in the molecule. It gives rise to an experimentally observed progression with a fundamental of +30 cm(-1) and an inverse anharmonicity. From the experimental data a shallow potential along the twist coordinate was derived for the S(1) state. For the shift vibration a wavenumber of +91 cm(-1) was observed, while +85 cm(-1) was computed. The ionisation energy of MHPC was determined to be 7.63 ± 0.05 eV using synchrotron radiation. When compared to earlier results on the parent compound [2.2]paracyclophane and pseudo-ortho-dihydroxy[2.2]paracyclophane it can be seen that already small variations in the substitution pattern have a significant impact on the shapes of the involved potential energy surfaces leading to strong variations in ground and excited state geometries and opto-electronic properties governing the exciton transfer processes.     

New rhenium(III) complexes with fluorinated β-diketones

Five new rhenium(III) complexes of the general formula ReCl₂(R_FCOCHCOR_F)(PPh₃)(OPPh₃), where R_F = CF₃ (I), C₂F₅ (II), C₃F₇ (III), C₄F₉ (IV), and CF₃CFOC₃F₇ (V), were synthesized. The known rhenium(V) complex ReOCl₂(OC₂H₅)(PPh₃)₂, which can readily be obtained from metallic rhenium, was used as a precursor. Two polymorphous modifications of compound I were found and studied by X-ray diffraction analysis. The thermal properties of the synthesized complexes were characterized by the DTA-TG method.     

The pH-controlled[2]or [3]pseudorotaxanes based on stilbene dye SD⊂CB[7]

We studied characteristics of [2] or [3]pseudorotaxanes based on stilbene dye SD?CB[7] . In neutral or weak alkaline conditions, SD could be encapsulated inside the stilbene site of CB[7] with 1:1 stoichiometry, whereas, with the pH changing to acidity, the hydrogen bonding between the carboxyl group and the carbonyl of CB[7] maked another CB[7] molecule include into hexanoic acid site, these processes were confirmed by fluorescence spectra,UV–Vis spectra and 1H NMR.     

CRYSTAL STRUCTURES OF 1,2-BENZO[2.2]PARACYCLOPHANE AND 1,2-BENZO[2.2]PARACYCLOPHANE-1,7-DIENE

<正> C20H16 (1) Mr = 256.34 and C20H14 (2), Mr = 254.32 are isomorphous, orthorhombic, P212121, Z = 4. For (?), ?a= 7.116(1), b =7.874(2), c = 24.564(4) A, V = 1376.4(3) A3, Dx = 1.237 g cm-3, μ(Mo-K α) =0.65 cm-1 , final R = 0.047 for 1152 observed reflections; for 2, a=6.963(2), b = 7.985(4), c = 24.315(8) A, V = 1351.9(8) A3, Dx = 1.250 g cm-3,μ(Mo-Kα) = 0.66 cm-1 , final R = 0.076 for 886 observed data. Structuralfeatures are similar to those of the parent [2.2]paracyclophane and related derivatives.     

Controlling Regioselectivity in Palladium-Catalyzed C−H Activation/Aryl–Aryl Coupling of 4-Phenylamino[2.2]paracyclophane

Selective activation/functionalization of C−H bonds has emerged as an atom- and step-economical process at the forefront of modern synthetic chemistry. This work reports palladium-catalyzed exclusively para-selective C−H activation/aryl–aryl bond formation with a preference over N-arylation under the Buchwald–Hartwig amination reaction of 4-phenylamino[2.2]paracyclophane. This innovative synthetic strategy allows a facile preparation of [2.2]paracyclophane derivatives featuring disparate para-substitutions at C-4 and C-7 positions in a highly selective manner, gives access to a series of potential candidates for [2.2]paracyclophane-derived new planar chiral ligands. The unprecedented behavior in reactivity and preferential selectivity of C−C coupling over C−N bond formation via C−H activation is unique to the [2.2]paracyclophane scaffold compared to the non-cyclophane analogue under the same reaction conditions. Selective C−H activation/aryl–aryl bond formation and sequential C−N coupling product formation is evidenced unambiguously by X-ray crystallography.     

Durable chiral sensor based on quartz crystal microbalance using self-assembled monolayer of permethylated β-cyclodextrin

A novel chiral sensor based on quartz crystal microbalance (QCM) with a self-assembled monolayer of permethylated β-cyclodextrin as the enantioselective coating has been derived which exhibit improved enantioselectivity and excellent long-term environmental stability when used in gas phase sensing.     

Synthesis of (7-polyfluoroalkyl)pyrazolo[1,5-a]pyrimidines based on lithium fluorine-containing β-diketonates

The reactions of Li enolates of fluorine-containing -diketones with 3-aminopyrazoles afforded (7-polyfluoroalkyl)pyrazolo[1,5-a]pyrimidines. The structure of 3-bromo-2-methyl-5-phenyl-7-trifluoromethylpyrazolo[1,5-a]pyrimidine was established by X-ray diffraction analysis.     

Synthesis,properties and crystal structures of volatile dimethylgold(III) complexes based on phenyl-containing β-diketones and β-iminoketone

We have synthesized and studied volatile dimethylgold(III) complexes based on phenyl-containing β-diketones and β-iminoketone, namely (CH₃)₂Au(C₆H₅–CO–CH–CO–CH₃), (CH₃)₂Au(bac) (1); (CH₃)₂Au(C₆H₅–CO–CH–CO–CF₃), (CH₃)₂Au(btfa) (2); and (CH₃)₂Au(C₆H₅–CO–CH–C(NH)–CH₃), (CH₃)₂Au(i-bac) (3). The obtained compounds were identified by elemental analysis, ¹H NMR and IR-spectroscopy, and were characterized by DTA and single-crystal X-ray diffraction studies. In compounds 2 and 3, the Au atom has a square coordination environment AuC₂O₂ and AuC₂NO, respectively.     

Some reactions of [(η6-C6Me6)Ru(η6-[2.2]paracyclophane)]-[BF4]2 with nucleophiles

Single addition of the nucleophiles X⁻ (X = H, CN, OH) to the less sterically hindered ring in [(η⁶-C₆Me₆)Ru(η⁶-C₁₆H₁₆)][BF₄]₂ (1) proceeds smoothly to produce, as the sole product, [(exo-η⁵-C₆Me₆X)Ru(η⁶-C₁₆H₁₆)][BF₄]. Use of Na[BD₄] in place of Na[BH₄] gives the expected shift in ν(C-H_exo) in the infrared spectrum.     

Reaction of [VO(OPr)3] with hexamethyldisylthiane in the presence of β-diketones

The reaction of [VO(OPr)₃] (Pr is n-propyl) with hexamethyldisylthiane Me₃SiSSiMe₃ in the presence of β-diketones (acetylacetone (HAcac), hexafluoroacetylacetone (Hfac), and dipivaloylmethane (Dpm)), is studied. In all cases, vanadium(IV) and vanadium(III) β-diketonate complexes of different types are formed. New crystalline modification [V(Acac)₃] is obtained in the reaction with HAcac. The mixedligand vanadium(III) complex of the composition [V₂(Hfac)₂(μ-OPr)]₂ is formed with Hfac. In the presence of Dpm, the known vanadium(IV) complex [V₂O₂(Dpm)₂(μ-OPr)₂] is obtained in which two vanadyl groups VO²⁺ are linked by two bridging propoxy groups. The structures of all products are determined by X-ray diffraction analysis.     

Synthesis of 4,5,6-trisubstituted 3-cyanopyridine-2(1H)-thiones based on α-substituted β-diketones

5-Substituted 3-cyano-4,6-dimethylpyridine-2(lH)-thiones were synthesized by the re action of a-substituted -diketones with cyanothioacetamide in the presence of triethyl amine. The compounds synthesized were converted into thieno[2,3-blpyridines by treatment with organic halides and KOH.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2719–2721, November, 1996.     

New stationary phase based on β-cyclodextrin for normal-phase HPLC group-separation of organic nitrates

The synthesis of a β-cyclodextrin-silica normal-phase (NP)-liquid chromatography (LC) stationary phase is reported. Silica gel was modified with (3-bromopropyl)trimethoxysilane to a 3-bromopropyl-silica that was reacted with β-cyclodextrin, resulting in a β-cyclodextrin-silica. To prove its usefulness in group-separation of organic nitrates among others, a mixture of three groups of organic nitrates was separated. The results are compared with those obtained on a nitrated polyol-silica that has recently been reported. The alkyl dinitrates exhibt higher retention relatively to alkyl mononitrates on the new phase. This allows to cut the LC fractions in a way that the alkyl mononitrates and phenylalkyl nitrates appear in one fraction and the dinitrates in a second one without any overlap of the two fractions. Received: 3 August 1999 / Revised: 27 September 1999 / Accepted: 30 September 1999     

Noncovalent columnar structures based on β-cyclodextrin

A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ～40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius R _h is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of R _h growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t ₀. At t > t ₀, R _h ∞ t ^0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors.     

Giant macrolactams based on β-sheet peptides

This paper reports the use of natural amino acids, the tripeptide β-strand mimic Hao, and the β-turn mimic δ-linked ornithine to generate water-soluble 54-, 78-, and 102-membered-ring macrolactams. These giant macrocycles were efficiently prepared by synthesis of the corresponding protected linear peptides, followed by solution-phase cyclization and deprotection. The protected linear peptide precursors were synthesized on 2-chlorotrityl chloride resin by conventional Fmoc-based solid-phase peptide synthesis. Macrocyclization was typically performed using HCTU and N,N-diisopropylethylamine in DMF at ca. 0.5 mM concentration. The macrocycles were isolated in 13-45% overall yield after HPLC purification and lyophilization. 1D, 2D TOCSY, and 2D ROESY (1)H NMR studies of the 54- and 78-membered-ring macrolactams establish that these compounds fold to form β-sheet structures in aqueous solutions.     

Preparation and enantioseparation characteristics of three chiral stationary phases based on modified β-cyclodextrin for liquid chromatography

In order to study the effect of the nature and the length of the spacer, three mixed 10-undecenoate/phenylcarbamate derivatives of β-cyclodextrin have been prepared and linked to allylsilica gel by means of a radical reaction. The chiral recognition ability of the resulting materials, when used as liquid chromatography chiral stationary phases (CSPs), was evaluated using heptane and either 2-propanol or chloroform as organic mobile-phase modifiers. A large variety of racemic compounds have been separated successfully on these CSPs (mainly pharmaceuticals and herbicides). Optimization of these separations was discussed in terms of mobile-phase composition and structural patterns of the injected analytes. The efficiencies of the three prepared materials were compared to those of previously described perphenylated-β-cyclodextrin column and to analogous cellulose derivative-based CSPs. Schematic illustration of the b-cyclodextrin/mandelic acid inclusion complex     

An improved synthesis of (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane

The resolution of the 4-acetyl[2.2]paracyclophane by the SAMP-hydrazone method is described. A new, short, high yield synthesis of both enantiomers (S)-(+)- and (R)-(−)-4-ethenyl[2.2]paracyclophane is reported.