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2-(2-Bromophenyl)ethyl groups have been used as building blocks in radical cyclisation reactions onto azoles to synthesise tri- and tetra-cyclic heterocycles. 2-(2-Bromophenyl)ethyl methanesulfonate was used to alkylate azoles (imidazoles, pyrroles, indoles and pyrazoles) for the synthesis of the radical precursors. Cyclisations of the intermediate aryl radicals yield new 6-membered rings attached to the azoles. The aryl radicals undergo intramolecular homolytic aromatic substitution onto the azole rings. Tributylgermanium hydride has been used with success to replace the toxic and troublesome tributyltin hydride. Initial studies show that the protocol can be used on solid phase resins. The molecular and crystal structures of methyl 5,6-dihydroimidazo[5,1-a]iso-quinoline-1-carboxylate and methyl 5,6-dihydroimidazo[2,1-a]isoquinoline-3-carboxylate were determined by X-ray crystallography. 相似文献
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Julian R. Osman Joe A. Crayston Allin Pratt David T. Richens 《Journal of Sol-Gel Science and Technology》2008,46(2):126-132
Mixed IrO2–TiO2 oxides were prepared by the sol–gel method by adding an aqueous solution of an iridium(III) acetate precursor [Ir3O(OAc)6 (HOAc)3]OAc, to titanium tetraethoxide in ethanol. By using an acetylacetonate modifier to stabilize the hydrolysed titanium alkoxide
and by omitting a catalyst, gels were produced in all cases. Transmission electron microscopy and EDX analysis confirmed the
high dispersion of iridium in the dried gel material on the nanometre scale. The images also show spherical cage features
up to 20 nm in diameter. High mass losses of the gels in the TGA scans suggested low degrees of hydrolysis of the acetate
precursor, but calcination gave a crystalline, mixed oxide (TixIr1–xO2) solid solution. The precursor is also soluble in ethanol, which provides a slightly modified route to similar materials. 相似文献
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We report a highly diastereoselective approach for the synthesis of the pentacyclic indole core of the manadomanzamine alkaloid skeleton, with complete control over the relative and absolute stereochemistries at the three contiguous stereocentres at ring positions 1, 10, and 24, from a readily available chiral template. 相似文献
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Steven M. Allin Liam J. Duffy Vickie McKee Michael J. McKenzie Oriol Bassas Joan Bosch 《Tetrahedron letters》2006,47(32):5713-5716
We report new and complementary routes for the highly stereoselective construction of functionalized benzoquinolizidine targets from readily available, non-racemic chiral templates. The methods developed allow us to predetermine relative product stereochemistries by judicious choice of substrate sub-structure, and provide ready access to alternative stereoisomers. 相似文献
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Pyrroloisoquinoline-based peptidomimetics are of significant interest in bioorganic chemistry as these targets are known to exhibit type II′ β-turn activity. In this paper we present a novel approach to such pyrroloisoquinoline templates based on a stereoselective N-acyliminium-mediated cyclization reaction to construct the heterocyclic core, coupled with an enolate amination protocol. We have applied both symmetrical and unsymmetrical electrophilic aminating reagents based on azodicarboxylate functionality, and demonstrate the utility of our approach in the synthesis of a peptide target. 相似文献
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Simple Zeros of the Riemann Zeta-Function 总被引:1,自引:0,他引:1
Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26. 相似文献
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We report a new asymmetric synthesis of the indole alkaloid derivative (+)-12b-epidevinylantirhine through stereoselective cyclization of a tethered indole nucleus onto an N-acyliminium ion intermediate, generated from a readily available non-racemic bicyclic lactam building block, and subsequent template modification through a highly diastereoselective conjugate addition protocol. In addition, we present the first X-ray crystal structure of this indole target. 相似文献