Synthese und Reaktionen des 5-[p-(Dimethylamino)phenyl]-2,2-dimethyl-4-phenyl-3-oxazolins

Synthesis and Reactions of 5-[p-(Dimethylamino)phenyl]-2,2-dimethyl-4-phenyl-3-oxazoline The title compound 8 has been synthesized in a one-pot reaction of 4′-(dimethylamino)benzoin ( 4 ) with 2-propanone and NH₃. The preparation of the intermediate 4 from 3 is the first example of an acid-catalyzed transformation of the stable benzoin 3 into the corresponding less stable benzoin 4 . Structures and yields of various by-products occurring under different reaction conditions during the synthesis of 8 from 4 are given. The O-atom of the 3-oxazoline ring in 8 could be replaced by S from P₂S₅ yielding the 3-thiazoline 14 . Separation of the enantiomers of the racemate 8 could only be performed by transforming them into the trimethylanilinium salts 8b and 8c of (−)- and (+)-10-camphorsulfonic acid, respectively. Solid NaOAc in boiling toluene caused the precipitation of the 10-camphorsulfonic acids from the quaternary ammonium salts as sodium salts and the removing of the third methyl group from the quaternary ammonium salts as AcOMe to give the enantiomers (−)-(5S)- 8 and (+)-(5R)- 8 . Their absolute configurations are deduced from an X-ray analysis of 8b .     

Synthesis, X-ray diffraction analysis and NMR studies of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol

The synthesis of (Z)-2-methyl-3-triphenylstannyl-3-pentene-2-ol and its characterization by an X-ray diffraction study and multinuclear NMR are reported. The tin atom exhibits a distorted tetrahedral SnC₄ geometry with the four Sn---C bond distances experimentally equivalent. The slight distortion from the ideal tetrahedral geometry is because of the presence of a weak intramolecular HO → Sn interaction of 3.012(3) Å which produces a loose four-membered ring. The title compound was characterized in solution by ¹H, ¹³C and ¹¹⁹Sn NMR, and the persistence of the weak intramolecular HO → Sn coordination in solution was revealed by ¹³C and ¹¹⁹Sn secondary isotope multiplet of partially labelled entities (SIMPLE-NMR) experiments.     

Volume and heat capacity of model non-aqueous self-assembly systems

Blends of immiscible polymers are often stabilized by block copolymers which can form non-aqueous micelles and microemulsions in the liquid polymers. The phase diagrans, apparent volumes and apparent heat capacities of model non-aqueous binary and ternary systems were studied in order to investigate the conditions under which such self-assembly systems could form. 1,2-Hexanediol, which can cosolubilize hexane and ethyleneglycol, forms inverse micelles in hexane and weak microaggregates in ethyleneglycol. Genapol X-060, a commercial alcoholic surfactant containing on the average an aliphatic chain of 13 carbons and 6 oxyethylenes (C₁₃E₆), forms microaggregates in poly(ethyleneglycol) 400. These self-assembly systems are strengthen in the presence of a third component which has an affinity for the inner phase.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Conversion directe des phospholes en dihydro-6,7 phosphepines dans la sphere de coordination du tungstene

In the presence of AlCl₃, [1-β-chloroethyl-3,4-dimethylphosphole]pentacarbonyltungsten($\text{1}$) rearranges into [1-chloro-3,4-dimethyl-6,7-dihydrophosphepin]pentacarbonyltungsten ($\text{3}$).     

Isotachophoretic analysis of the dihydrofolate reductase reaction in the presence of methotrexate and ascorbic acid

The antifolate methotrexate (MTX) is widely used in cancer chemotherapy. In this study, we show that MTX (MTX-Glu1) and MTX-polyglutamates (MTX-Glu2-5) strongly inhibited the growth of the leukemic cell line MOLT-4. This effect, however, was mitigated by ascorbic acid. We investigated whether ascorbic acid is able to reduce dihydrofolic acid (DHF) to tetrahydrofolic acid (THF) directly or by circumventing the MTX inhibition of dihydrofolate reductase (DHFR). The inhibition of this NADPH-dependent reduction of DHF by MTX-Glun in the absence or presence of ascorbate, was determined by analytical isotachophoresis. Using 0.01 M HCl/histidine, pH 6.0, as a leading electrolyte (L) and 0.005 M 2-(N-morpholino)ethanesulfonic acid (MES)/histidine, pH 6.0, as a terminating electrolyte (T), MTX-Glun derivatives including MTX-Glu1 could be easily separated, whereas the quantitative estimation of THF was not possible. A quantitative characterization of the DHFR reaction by measuring NADPH, NADP+ and ascorbate was achieved with another system (L: 0.01 M HCI/beta-alanine, pH 3.73; T: 0.01 M caproic acid, pH 3.27). Nanomolar concentrations of MTX-Glu1-5 inhibited consumption of NADPH and production of NADP+. Ascorbic acid was not able to reduce DHF, neither directly nor after inhibition of DHFR by MTX. However, ascorbic acid seemed to diminish the oxidation of THF and this may account for its capacity to reduce the inhibitory effect of MTX on MOLT-4 cells.     

Formic acid oxidation on Pd/RuO2: does the RuO2 support enhance the electrocatalytic activity of Pd nanoparticles?

Journal of Solid State Electrochemistry - The aim of this work was to study the effect of a RuO2 support on the activity of Pd nanoparticles for formic acid oxidation, comparing the results with...     

1,1,2,2-Tetraethynylethanes: Synthons for Tetraethynylethenes and Modules for Acetylenic Molecular Scaffolding

The synthesis of functionalized 1,1,2,2-tetraethynylethanes (= 3,4-diethynylhexa-1,5-diynes) as synthons for tetraethynylethenes (3,4-diethynylhex-3-ene-1,5-diynes) and as building blocks for three-dimensional acetylenic molecular scaffolding targeting the synthesis of the molecular carbon belts 3 and 4 is reported (Scheme 1). Reaction of diethyl oxalate and (trialkylsilyl)ethynyl Grignard reagents afforded the silyl-protected 3,4-diethynylhexa-1,5-diyne-3,4- diols 7 and 8 which were transformed in high yields into the cyclic carbonate 9 and the cyclic orthoesters 10–13 , respectively (Scheme 2). The solid-state structures of 9 and 10 were elucidated by X-ray crystallography. The alkyne protecting groups in 9, 10 , and 12 were smoothly removed to give the free tetraynes 14–16 as relatively stable oils in nearly quantitative yields (Scheme 3). Orthoesters 15 and 16 underwent Pd-catalyzed cross-coupling with iodobenzene to give the tetraphenyl derivatives 17 and 18 (Scheme 4). Thermal acid-catalyzed elimination of the orthoester moieties in 12 and 13 produced the silyl-protected tetraethynylethenes 19 and 20 and concluded a novel, simple three-step synthesis of these fully two-dimensionally conjugated π-chromophores (Scheme 5).     

Improved Purification of C60 and Formation of σ- and π-Homoaromatic methano-bridged fullerenes by reaction with alkyl diazoacetates

A rapid and inexpensive method for the large-scale purification of C₆₀ is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C₆₀ with ethyl and tert-butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene-bridged isomers 1a – 3a and 1b – 3b , respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b , respectively. Isomers 1a / b possess the methano bridge at the 6–6 ring junction, whereas structures 2a / b and 3a / b are bridged at the 6–5 junction. A dramatic influence of local and π-ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a / b and over a hexagon ring in 3a / b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the ¹³C-NMR chemical shifts of the bridgehead C-atoms and the ¹J(C,H) coupling constants for the methano-bridge atoms reveals conclusively that the 6-5-ring-bridged structures 2a / 2b and 3a / 3b are π-homoaromatic (‘open’ transannular bond) and the 6-6-ring-bridged structures 1a / b are π-homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π-homoconjugation in 2a / b and 3a / b represents a much smaller electronic perturbation of the original C₆₀ chromophore than σ-homoconjugation in 1a / b . The results of this study demonstrate an impressive linkage between the chemistry of methano-bridged annulenes and methano-bridged fullerenes.     

Catalytic Cyclophanes. Part VIII. Cytochrome P-450 activity of a porphyrin-bridged cyclophane

Following a known synthetic procedure, the porphyrin-cyclophane 1 having a porphyrin attached by two straps to an apolar cyclophane binding site was prepared. Upon metallation, the Zn^II and Fe^III derivatives 2 and 3 , respectively, were obtained in good yields. Treatment of 3 with base yielded the μ-oxo dimer 4 in which the two oxo-bridged porphyrins moieties are both capped by cyclophane binding sites. All compounds 1–4 are freely soluble in protic solvents such as MeOH and CF₃CH₂OH, and the Fe^III derivatives 3 and 4 are active cytochrome P-450 mimics in these protic environments. Strong inclusion complexation of polycyclic aromatic hydrocarbons by 1 and 3 in alcoholic solvents was observed and quantified by ¹H-NMR and UV/VIS titrations. Acenaphthylene binds in an ‘equatorial’ orientation which locates its reactive 1,2-double bond near the porphyrin center, whereas phenanthrene binds ‘axially’ with the reactive 9,10-double bond oriented away from the porphyrin. The reduction potential of 3 was not significantly altered by substrate binding. In the unbound form, the Fe^III center in porphyrin 3 was found by ESR and ¹H-NMR to prefer a high-spin state (S = 5.2). In CF₃CH₂OH, using iodosylbenzene as O-transfer agent, the Fe^III derivative 3 catalyzed the oxidation of acenaphthylene to acenaphthen-1-one ( 14 ). Phenanthrene inhibited the reaction, possibly as a result of strong but nonproductive binding. Under similar conditions, isotetralin ( 18 ) was aromatized with high turnover to 1,4-dihydronaphthalene. The μ-oxo dimer 4 also showed high activity in the oxidation of acenaphthylen in MeOH, a result which provides strong evidence for efficent supramolecular catalysis. Due to as yet unknown reaction channels leading to polymeric products, poor mass balances were generally obtained in the oxidations effected in MeOH and CF₃CH₂OH in the presence of PhIO.     

Large Water-Soluble Cyclophanes with Convergent Intracavity Functionality

New tricyclic spacers, readily available through fourfold Mannich reaction of substituted dibenzyl ketones, were introduced into a series of ten H₂O-soluble cyclophanes with spacious preorganized cavity binding sites. These spacers provide H₂O-solubility with amine or crown-ether functionality remote from the cyclophane cavity while directing functional groups such as keto or OH groups in a precise geometrical array inside the cavity. The cyclophanes were designed to include organic substrates via a combination of apolar and specific polar functional group interactions. The X-ray crystal-structure analysis of the tritopic receptor 18 with one potential neutral-molecule and two cation-binding sites showed a large rectangular open cavity with dimensions of roughly 9 × 14 Å and a spacing of 9.7 Å between the O-atoms of two convergent C?O groups. Despite the binding-site preorganization, cyclophanes incorporating two of the new spacers did not show any substrate binding in aqueous solutions. The failure of these systems to function as receptors is mainly due to steric hindrance to important cyclophane aromatic ring-guest interactions. Also, the favorable solvation of the intracavity functionality may prevent the formation of complexes. Hybrid receptors constructed from the novel spacers and diphenylmethane units were found to bind flat aromatic substrates as well as bulky [4.2]paracyclophanes. The observed large differences in stability (ΔΔG°> 2 kcal mol^?1) of the complexes formed by three structurally closely related hybrid receptors with convergent C?O, OH or CH₂ groups and 6-hydroxynaphthalene-2-carbonitrile as guest can be explained by a strong solvation effect of the convergent functional groups on apolar inclusion complexation.