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[structure: see text] The first enantioselective total synthesis of (-)-Centrolobine is described. The key reaction is the synthesis of the cis-disubstituted tetrahydropyran framework by intramolecular cyclization of the enantiopure hydroxyketone 3 with Et3SiH and TMSOTf. The stereoselective reduction of the beta-ketosulfoxide 4 is the source of chirality. Revision of the absolute configuration of (-)-Centrolobine is proposed. 相似文献
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Carreño MC Des Mazery R Urbano A Colobert F Solladié G 《The Journal of organic chemistry》2003,68(20):7779-7787
The stereocontrolled formation of cis-2,5-disubstituted tetrahydrofurans and cis-2,6-disubstituted tetrahydropyrans is achieved from enantiopure ketosulfinyl esters by reduction, Weinreb's amide, and ketone formation, followed by the reductive cyclization (Et3SiH/TMSOTf) of the resulting hydroxysulfinyl ketones. The sulfoxide-bearing heterocycles were transformed into two natural products, (-)-centrolobine (1) and both enantiomers of cis-(6-methyltetrahydropyran-2-yl)acetic acid (2). 相似文献
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A modification of the material law associated with the well‐known Biot system as suggested by Murad and Cushman (Int. J. Eng. Sci. 1996; 34(3):313–338) and first investigated by Showalter (J. Math. Anal. Appl. 2000; 251(1):310–340) is reconsidered, generalized and analysed in the light of a new approach to a comprehensive class of evolutionary problems. The framework allows a uniform approach to problems involving general anisotropic, inhomogeneous, non‐smooth media thus covering, for example, transmission problems in layered materials. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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David B. Lovejoy Des R. Richardson Paul V. Bernhardt 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):341-342
The potentially tridentate O,N,S‐donor ligand, 2‐hydroxy‐1‐naphthaldehyde 2‐methylthiosemicarbazone, C13H13N3OS, has been structurally characterized and the molecule is found to exhibit a distorted planar structure with the thiosemicarbazide moiety being twisted slightly out of the plane defined by the naphthyl ring. 相似文献
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Ohne Zusammenfassung 相似文献
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In this paper three‐dimensional lubrication flow of grease is analysed numerically. The lubrication flow configuration is formed by two ellipsoid rollers. The load is assumed to be light enough for the lubrication mode to be purely hydrodynamic. The fluid behaviour is modelled using the Herschel–Bulkley model, and a two‐dimensional modified Reynolds equation is derived. The numerical solutions are obtained by using a hybrid spectral/iterative technique and the Galerkin projection scheme. The effects of the material and geometrical parameters on pressure distribution are emphasized in the study. The investigation is conducted for a situation where the two ellipsoids are fully immersed in a grease lubricant. The effect of the geometry on the pressure distribution is determined by varying the ratio of the semi‐axes and the minimum gap of the two rollers, respectively. The effect of the material parameters is examined by varying the power‐law index and yield stress. It is found that the pressure distribution is strongly influenced by the shape of the rollers, the size of the minimum gap of the rollers and the rheological parameters. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献