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The pyrrolidine natural products, plakoridines A and B, as well as an array of unnatural analogues, have been prepared using a five-step synthetic sequence modelled on a biogenetic theory. The key transformation involves a ‘Mannich/Michael/internal-redox’ cascade, which proceeds in yields of 31-63%. 相似文献
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The combination of two or more generalized Crank Nicolson schemesin order to obtain second, third and fourth order accurate discretizationsin time is considered. Particular attention is given to thestability properties of the methods proposed. 相似文献
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Gourlay & Morris (1970) presented a multistep formulationof a scheme proposed by Strang (1968) for the numerical solutionof non-linear hyperbolic systems. This formulation did not takeaccount of given boundary data and led to instability in certainproblems. This note presents boundary techniques for the incorporationof the given boundary data and in numerical experiments, itis shown that the instabilities, which arose in the problemsof Gourlay & Morris, are prohibited. 相似文献
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Ring Homomorphisms and Finite Gorenstein Dimension 总被引:2,自引:0,他引:2
The local structure of homomorphisms of commutative noetherianrings is investigated from the point of view of dualizing complexes.A concept of finite Gorenstein dimension, which substantiallyweakens the notion of finite flat dimension, is introduced forhomomorphisms. It is shown to impose structural constraints,due to a remarkable equivalence of subcategories of the derivedcategory of all modules. An essential part of this study is the development of relativenotions of dualizing complexes and Bass numbers. It is provedthat the Bass numbers of local homomorphisms are rigid, extendinga known result for local rings. Quasi-Gorenstein homomorphismsare introduced as local homomorphisms that base-change a dualizingcomplex for the source ring into one for the target. They areshown to have the stability properties of the Gorenstein homomorphismthat they generalize. 1991 Mathematics Subject Classification:primary 13H10, 13D23, 14E40; secondary 13C15. 相似文献
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An expedient synthetic route to the fully substituted pyrrolidine ring system of the plakoridines is described using an approach modeled on a plausible biosynthetic pathway. 相似文献