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171.
An effcient formal synthesis of(+)-tashiromine was achieved by employing an intermolecular asymmetric Mannich-type reaction as the key step.Concurrently,a novel approach toward the total synthesis of(+)-stemoamide through dyotropic rearrangement of 3,4-cis-b-lactone was also explored. 相似文献
172.
《Tetrahedron》2013,69(36):7592-7607
A formal synthesis of didehydrostemofoline and isodidehydrostemofoline has been accomplished by preparing an intermediate in the Overman synthesis of these alkaloids from commercially available 2-deoxy-d-ribose. The work presented in this account chronicles the evolution of our explorations to identify the optimal steric and electronic control elements necessary to generate the tricyclic core structure of these alkaloids in a single operation from an acyclic precursor. The key step in the synthesis is a novel dipolar cycloaddition cascade sequence that is initiated by cyclization of a rhodium-derived carbene onto the nitrogen atom of a proximal imine group to generate an azomethine ylide that then undergoes spontaneous cyclization via dipolar cycloaddition. The synthesis features several other interesting reactions, including a Boord elimination to prepare a chiral allylic alcohol, a highly diastereoselective Hirama–Itô cyclization, and a useful modification of the Barton decarboxylation protocol. 相似文献
173.
C. J. Toussaint F. Bo 《International journal of environmental analytical chemistry》2013,93(1-2):55-67
Abstract In the framework of remote sensing studies concerning coastal transport of pollution in the Northern Adriatic Sea, a method has been developed for the quantitative determination of sulphur, iron, titanium, calcium, phosphorus, silicon, aluminium, magnesium in suspended matter of sea water. The suspended material was collected by filtering on millipore membrane filters with pore width of 0.45 μ and directly analysed by X-ray spectroscopy. For calibration dried solution and particulate standard samples were used. Limits of sensitivity and precision of the method are reported. Correlations between the concentration of these elements and the total suspended matter/chlorophyll are discussed. The aim is to study the geochemical composition of particulate matter and its variations within the geographical site of the sea basin and the seasonal conditions. The approach is to consider aluminium and the other elements normalized on Al. On the basis of a matrix correlation analyses of some sets of data chosen in the restricted area for investigation, some hypothesis on superficial distribution of clay, carbonate, iron hydrous oxides and other mineral detrites, are taken into account. The results confirm the complex situation existing in the offshore area of the Venice lagoon from a geochemical point of view. The suspended matter seem to be argillaceous in the Southern part of the investigated area and semi-argillaceous with hydrous oxides and carbonates in the Northern part which is influenced by the Piave river. 相似文献
174.
Brian Murphy Peter Mcloughlin 《International journal of environmental analytical chemistry》2013,93(7-8):653-662
The potential of an optical sensor based on mid-infrared spectroscopy, utilising a zinc selenide (ZnSe) attenuated total reflectance (ATR) element coated with an amorphous Teflon polymer, to determine chlorinated hydrocarbon species (CHC) in an aqueous environment is examined. The polymer coating concentrates the analytes within the penetration depth of the Fourier transform infrared (FTIR) evanescent wave and excludes water from the region. Teflon AF (Amorphous Fluoropolymer) is a family of amorphous copolymers based on polytetrafluoroethylene (PTFE), and is commercially available in two polymeric grades. Teflon AF is highly amorphous in nature with a large 'void volume', exhibits excellent chemical resistance and low water absorption. Such properties identify it as an excellent candidate for enrichment coating on an ATR/FTIR sensor. The potential of both polymeric grades of Teflon AF as enrichment membranes for ATR/FTIR analysis of CHC species was examined and contrasted. A rapid, repeatable, reversible response was observed with both grades to a range of CHC species. Linear responses in the mg/L region, with detection limits in the low mg/L region were achieved with the system used. 相似文献
175.
176.
Classical problems in integral geometry and geometric probability involve the kinematic measure of congruent segments of fixed length within a convex body in R3. We give this measure from rotational formulae; that is, from isotropic plane sections through a fixed point. From this result we also obtain a new rotational formula for the volume of a convex body; which is proved to be equivalent to the wedge formula for the volume. 相似文献
177.
Guang Gui Ding 《数学学报(英文版)》2015,31(12):1872-1878
In this article, we use some analytic and geometric characters of the smooth points in a sphere to study the isometric extension problem in the separable or reflexive real Banach spaces. We obtain that under some condition the answer to this problem is affirmative. 相似文献
178.
For every , we present a set of points in the plane such that every planar 3-tree with n vertices has a straight-line embedding in the plane in which the vertices are mapped to a subset of . This is the first subquadratic upper bound on the cardinality of universal point sets for planar 3-trees, as well as for the class of 2-trees and serial parallel graphs. 相似文献
179.
Tian Jin Jin-Seok Kim Yu Mu Seok-Hwi Park Xiangdan Jin Jong-Cheol Kang Chang-Young Oh Won-Hun Ham 《Tetrahedron》2014
Total synthesis of methyl l-daunosaminide hydrochloride was achieved from readily available l-tyrosine. Key steps in this strategy were palladium(0) catalyzed stereoselective intramolecular oxazine formation and catalytic hydrogenation of oxazine intermediate. This paper reported 1H and 13C NMR data of α- and β-anomer of methyl l-daunosaminide hydrochloride. 相似文献
180.
Hu Yuan Kaijian Bi Wanlin Chang Rongcai Yue Bo Li Ji Ye Qingyan Sun Huizi Jin Lei Shan Weidong Zhang 《Tetrahedron》2014
A total synthesis of Daphnodorin A, a member of the Daphnodorins, was accomplished. Key features of the synthetic strategy include construction of 2-substituted-3-functionalized benzofuran via intramolecular Heck reaction and a mild Barton–McCombie deoxygenation process mediated by triethylborane. The total synthesis provided Daphnodorin A in 19.7% or 5.6% overall yield over 7 or 15 steps. 相似文献