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At least 127 records · Page 7Linked to original sources
PubMed2000

A three-component coupling strategy for tetrahydrofuran synthesis: application of the diisopropyl tartrate modified (E)-gamma-(dimethylphenylsilyl)allylboronate as an alpha,gamma-allyl dianion equivalent.

[reaction: see text] A highly convergent three-component coupling strategy for the stereocontrolled synthesis of 2,3,5-trisubstituted tetrahydrofurans is described. After allylboration of the first aldehyde with 1, the chiral, nonracemic allylsilanes 2 are coupled with a second aldehyde or ketone with Lewis acid catalysis to give tetrahydrofurans 3 or 4 with excellent selectivity. The 2,5-stereochemistry is controlled by operating under nonchelate (e.g., 3) or chelate (e.g., 4) conditions.

Allyl Compounds↗
PubMed2001

Stereo- and regioselective radical cyclization of 6-(bromomethyl)dimethylsilyl-1',2'-unsaturated uracil nucleosides: synthesis of 1'-alpha-hydroxymethyl nucleosides.

Mode of radicalcyclization (5-exovs. 6-endo) was investigated by using 6-(bromomethyl)dimethylsilyl derivatives of 1',2'-unsaturated uridine with an aim to develop a new stereoselective method for the introduction of an alpha-hydroxymethyl group at the anomeric position. Although the 2'-unsubstituted derivative underwent only 6-endo-cyclization, substrates bearing 2'-CO2Me or 2'-OBz group gave exclusively 5-exo-cyclized products with a high stereoselectivity.

Bromine Compounds↗
PubMed1983

[Use of silatranes in combination with Vishnevskii'n ointment in wound treatment].

Experiments on rats were performed to study the effect of I-/chlormethyl/silatrane and I-/ethoxy/silatrane as well as that of triethanolamine and /chlormethyl/triethoxysilane on the biochemical characteristics of granular-fibrous tissue. The drugs were applied to the wound in the form of liniments. Silatranes stimulated cell proliferation and raised biosynthetic activity of the cells. They also favoured collagen and non-collagenous protein accumulation and reduced the inflammatory manifestations. The silicon-containing fragment of the silatrane molecule, /chlormethyl/triethoxysilane, produced an analogous but less pronounced action. Triethanolamine containing no silicon appeared to be far less active. These data indicate that the presence of silicon in the silatrane grouping is of great importance for its effective biological function.

Animals↗
PubMed2002

Metal-catalyzed silacyclopropanation of mono- and disubstituted alkenes.

As an alternative to the strongly reducing conditions necessary for the formation of silacyclopropanes, silylene transfer was developed as a mild, functional group tolerant method of silacyclopropanation. Complex silacyclopropanes were formed from functionalized alkenes using cyclohexane di-tert-butyl silacyclopropane, 1, as the source of t-Bu(2)Si. Di-tert-butyl silylene can be generated from 1 through the use of a catalytic amount of a metal salt. At -27 degrees C, silver triflate catalyzes the transfer of t-Bu(2)Si from 1 to mono- and disubstituted alkenes stereospecifically and diastereoselectively. In situ functionalization of silacyclopropanes with catalytic zinc bromide and methyl formate provides for an expedient one-flask synthesis of complex oxasilacyclopentanes from alkenes.

Alkenes↗
PubMed2006

Nonracemic 3 degrees-carbamines from the asymmetric allylboration of N-trimethylsilyl ketimines with B-allyl-10-phenyl-9-borabicyclo[3.3.2]decanes.

The simple and efficient asymmetric synthesis of 3 degrees -carbamines 7 from N-TMS enamines (3) and either enantiomeric form of beta-allyl-10-(phenyl)-9-borabicyclo[3.3.2]decane (1) is reported. The high reactivity (<1 h, -78 degrees C) and enantioselectivity (60-98% ee) of these substrates can be attributed to the fact that the complexation of 3 with 1 facilitates its isomerization to the corresponding syn-N-TMS ketimine complex from which allylation can occur. In addition to providing the homoallylic amines 7 with predictable stereochemistry, the procedure also permits the efficient recovery of the chiral boron moiety (50-65%) as air-stable crystalline pseudoephedrine complexes 8, which are directly converted back to 1 with allylmagnesium bromide in ether (98%).

Allyl Compounds↗
PubMed2004

Formation of dispersed nanostructures from poly(ferrocenyldimethylsilane-b-dimethylsiloxane) nanotubes upon exposure to supercritical carbon dioxide.

While incompatible block copolymers commonly assemble into several established classical or complex morphologies, highly asymmetric poly(ferrocenyldimethylsilane-b-dimethylsiloxane) (PFS-b-PDMS) diblock copolymers can also self-organize into high-aspect-ratio nanotubes with PDMS corona in the presence of PDMS-selective organic solvents. Exposure of these nanotubes on a carbon substrate to supercritical carbon dioxide (scCO2), also a PDMS-selective solvent, appears to promote partial dissolution of the copolymer molecules. At sufficiently high copolymer concentrations, the dissolved molecules subsequently re-organize within the scCO2 environment to form new copolymer nanostructures that redeposit on the substrate upon scCO2 depressurization. Transmission electron microscopy reveals that micelles form under all the conditions examined here, whereas nanotubes coalesce and vesicles develop only at relatively high temperatures. The extent to which the copolymer nanotubes dissolve and the size distribution of the replacement micelles are sensitive to exposure conditions. These results suggest that the phase behavior of PFS-b-PDMS diblock copolymers in scCO2 may be remarkably rich and easily tunable.

Carbon Dioxide↗
PubMed1983

[Silatranes as stimulators of the development of granulation tissue].

Experiments on rats were made to study the effect of I-(chloromethyl) silatrane and I- (ethoxy) silatrane and that of triethanolamine and chloromethyl triethoxysilane on biochemical parameters of granular-fibrous tissue. The preparations were applied to a wound defect in the form of liniments. Silatranes were found to stimulate proliferation of the cells and to increase their biosynthetic activity, to favour accumulation of collagen and non-collagenic proteins, and reduction of the inflammatory phenomena. The silicon-containing fragment of the silatrane molecule chloromethyl triethoxysilane produced an analogous but less marked action. Triethanolamine containing no silicon was found to be as less active. These data indicate that silicon entering the silatrane grouping is of great importance for the occurrence of its biological activity.

Animals↗
PubMed2004

Biocatalysis in the development of functional polymer-ceramic nanocomposites.

Fluorescent silica/polymer nanocomposites have been synthesized by condensing tetramethyl orthosilicate (TMOS) around fluorescent polymer strands of poly(2-naphthol). The polymer is biocatalytically synthesized via peroxidase catalyzed polymerization in micelles of the cationic surfactant, cetyltrimethylammonium bromide (CTAB). Silica condensation at the micelle-water interface results in encapsulation of the polymer. Fluorescence spectroscopy and fluorescent light microscopy provide critical evidence that the polymer luminescence properties are conferred to the composite material. The fabrication of polymer entrapped in ordered, mesoporous materials represents a viable step toward the development of functional polymer-ceramic nanocomposites.

Catalysis↗
PubMed2003

Mechanism of cis-enamide formation from N-(alpha-silyl)allyl amides: synthetic potential of stepwise dyotropic rearrangements.

A novel transformation of silyl amides to N-cis-propenyl amides was recently reported, the reaction of which is a formal 10-electron double sigmatropic, or dyotropic, rearrangement. Density functional calculations (B3LYP/6-311++G(3d,3p)//B3LYP/6-31G(d)) have been carried out to investigate the mechanism of this reaction. A two-step process involving sequential 1,4-silyl and 1,4-hydrogen shifts is predicted. The 1,3-dipolar azomethine ylide intermediate profits from charge stabilization by allylic resonance and phenyl conjugation. The consecutive thermal migration of two sigma-bonds (stepwise dyotropic rearrangement) is an example of a host of reactions with synthetic potential.

Allyl Compounds↗
PubMed2003

Application of silicon-based cross-coupling technology to triflates.

Aryl silatranes undergo fluoride-induced cross-coupling with aryl triflates to provide unsymmetrical biaryl derivatives in good to excellent yields. Silatranes also couple with aryl iodides and bromides, although the yields of adduct are lower than with the corresponding siloxane derivates. Aryl siloxanes (which had previously failed to couple with triflates) can be employed for triflate couplings using the Denmark modification, although the yields are lower than the corresponding silatrane reactions.

Biphenyl Compounds↗
PubMed2005

Highly photoluminescent multilayer QD-glass films prepared by LbL self-assembly.

A novel and facile preparation method for layer-by-layer (LbL) self-assembled films incorporating quantum dots (QDs) and having intense photoluminescence (PL) from blue to red is presented. Functional sol-gel-derived glass layers prepared by the hydrolysis of 3-aminopropyltrimethoxysilane (APS) or 3-mercaptopropyltrimethoxysilane (MPS) have been used as a linkage between QD layers. Absorption, PL spectroscopy, transmission electron microscopy, and atomic force microscopy were employed for characterization, which revealed that the QDs in the prepared films had a nearly close-packed coverage and were not aggregated. The PL efficiencies of the QDs (CdTe or ZnSe, both are thioglycolic acid-stabilized) dispersed in the films were roughly half that of the initial colloidal solutions but reached 24% before a refractive index correction. The thickness of the red-emitting film with 10 CdTe QD layers was approximately 50 nm. The concentration of QDs in the film derived from the first absorption peak was approximately 0.01 M. Because the PL starts to show a red shift, the obtained concentration is practically the ultimate one in the glass matrix. The mercapto, amino, and carboxyl groups play important roles in LbL self-assembling processes.

Cadmium Compounds↗
PubMed1995

Metabolic pathways of 4-[(3-methoxyphenyl)methyl]-2,2,6,6-tetramethyl-1-oxa-4-aza-2,6- disilacyclohexane (MPSC) hydrochloride, a silicon-containing xenobiotic, in rat, dog, and man.

1. The metabolic pathways of Sandoz compound 58-112, 4-[(3-methyoxyphenyl)-methyl]-2,2,6,6-tetramethyl-1-oxa-4-aza-2,6- disilacyclohexane (MPSC) hydrochloride were evaluated in rat, dog, and man after a single oral dose. 2. In rat, dog and man the major route of elimination was renal. In the dog, renal excretion of unchanged MPSC represented a substantial portion of the dose whereas in rat and man MPSC was completely metabolized prior to excretion. 3. In rat and man, the major end-product metabolite was 3'-[((hydroxydimethylsilyl)-methylamino)methyl]-phenol glucuronide; 4-[(3-hydroxyphenyl)-methyl]-2,2,6,6-tetramethyl-1-oxa-4-aza-2,6- disilacyclohexane and 4-[(4-hydroxy-3-methoxyphenyl)-methyl]-2,2,6,6-tetramethyl-1-oxa-4-aza-2 ,6- disilacyclohexane and their conjugates were also present. In dog, the major end-product metabolites were the hippurate of 3-methoxybenzoic acid and 3-hydroxybenzoic acid.

Animals↗
PubMed2001

[Preparation and chromatographic characteristics of octadecyl bonded titania stationary phase for high performance liquid chromatography].

Porous titania microspheres (surface area: 36.7 m2/g, average pore volume: 0.30 mL/g, average pore diameter: 32.2 nm, average diameter: 3.5 microns) with a very narrow particle size distribution, were synthesized by refluxing polymerized-induced colloid aggregation (PICA), with octadecyltrimethoxysilane in toluene as a solvent for 8 h, and octadecyltitania stationary phase (ODT) was obtained. The carbon content and hydrophobic selectivity of the stationary phase were 2.87% (i.e. 0.66 mumol/m2) and 0.4638, respectively. ODT showed good chromatographic performances when it was used to separate the neutral and basic solutes using methanol solution as a mobile phase.

Aniline Compounds↗
PubMedDate not supplied

[1-Ethoxysilatrane: ulcerostatic effect and its possible mechanisms].

Stimulating effect of I-ethoxy silatrane on healing of acetate derived stomach ulcer was studied in rats. The drug was shown to inhibit lipid peroxidation and free-radical oxidation in blood and gastric tissues as well as to accelerate reparation in ulcerous zone. I-Ethoxy silatrane interacted with artificial membranes and affected the respiration rate in liver mitochondria. Membranetropic effect of I-ethoxy silatrane appears to be involved in the drug ulcerostatic effect.

Animals↗
PubMed2005

An approach for fabricating self-assembled monolayer of Ag nanoparticles on gold as the SERS-active substrate.

In this paper, an approach for fabricating an active surface-enhanced Raman scattering (SERS) substrate is adopted. This approach is based on the assembling of silver nanoparticles film on gold substrate. Rhodamine 6G (R6G) and p-aminothiophenol (p-ATP) were used as probe molecules for SERS experiments, showing that this new active substrate has sensitivity to SERS response. Tapping-mode atomic force microscopy (AFM) was also used to investigate the surface morphology following the fabricating process of the active SERS substrate, which showed that large quantities of silver nanoparticles were uniformly coated on the substrate.

Aniline Compounds↗
PubMed2003

Unexpected syn hydride migration in the non-aldol aldol reaction.

[structure: see text] Non-aldol aldol rearrangement of the epoxy silyl ether 13b afforded the expected anti methyl ketone 14, while the diastereomeric epoxy silyl ether 13a afforded the syn methyl ketone 8b via an unprecedented syn hydride migration. Calculations suggest that this unusual reaction proceeds via the carbocation, which cannot easily rotate due to steric hindrance.

Aldehydes↗