Polystyrenes with Chiral Phosphoramide Substituents as Lewis Base Catalysts for Asymmetric Addition of Allyltrichlorosilane: Enhancement of Catalytic Performance by Polymer Effect.
ABSTRACT In the asymmetric addition of allyltrichlorosilane to benzaldehyde, polystyrenes with chiral phosphoramide substituents as Lewis base catalysts showed up to 2.4 times better catalytic activity and 1.4 times higher enantioselectivity than the corresponding low-molecular-weight analogues.
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ABSTRACT: This review article is divided in two parts. In the first part (Sections 2 and 3) selected examples of the publications that appeared in the literature in the period 2003-2005 in the field of immobilized organic catalysis are presented. When appropriate, the results of these publications are compared to those reported earlier and already discussed in a previous review article (see ref.()). On the basis of this survey, in Section 4 some general considerations about when and why a supported version of an organic catalyst is worth developing are proposed. In Section 4 a list of suggestions about how the process of immobilization should be carried out is also included, taking into account several factors such as the properties of the catalyst, the nature of the support, and the mode of connection of the catalyst to the support. 1 Introduction 2 Achiral Organic Catalysts 2.1 Catalysts for Oxidation Reactions 2.2 Lewis Base Catalysts 2.3 Acid Catalysts 2.4 Thiazolium Salts 2.5 Miscellaneous Catalysts 2.6 Bifunctional Catalysts 3 Chiral Organic Catalysts 3.1 Catalysts for Oxidation Reactions 3.2 Lewis Base Catalysts 3.3 Catalysts Derived from Cinchona Alkaloids 3.4 Catalysts Derived from Amino Acids 4 A Short Discussion on the Practical Aspects of Catalyst Immobilization 4.1 When? 4.2 Why? 4.3 How? 5 ConclusionsAdvanced Synthesis & Catalysis 10/2006; 348(12‐13):1367 - 1390. DOI:10.1002/adsc.200606096 · 5.54 Impact Factor
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ABSTRACT: Crosslinked polystyrene-supported resins 4, 7a, and 7b containing N-sulfonylated beta-amino alcohol in 98, 20, and 40% loadings are prepared. Asymmetric diethylzinc additions to benzaldehyde employing titanium complexes of 10 mol % resins 4, 7a, or 7b are examined and the best performed 7a/Ti(O-i-Pr)4 catalytic system applies to various aldehydes to afford desired secondary alcohols in excellent enantioselectivities up to 95% ee. The resin 7a is reused five times, giving the product with enantioselectivities >or=86% ee and an 81% ee is obtained when the resin is used the sixth time. The used resin 7a is refreshed with 1 M HCl and the asymmetric reaction employing the regenerated resin 7a gives the product in 88% ee.Chirality 01/2007; 19(1):10-5. DOI:10.1002/chir.20332 · 1.72 Impact Factor
Article: Asymmetric Organocatalysis[Show abstract] [Hide abstract]
ABSTRACT: This review is intended to update the impressive amount of recent developments of asymmetric organocatalysis in numerous reaction types, such as nucleophilic additions to electron-deficient CC double bonds, nucleophilic additions to CO double bonds, nucleophilic additions to CN double bonds, nucleophilic additions to unsaturated nitrogen, nucleophilic substitutions at aliphatic carbon, cycloaddition reactions, oxidations, reductions, kinetic resolutions and miscellaneous reactions, covering the literature from 2005 to 2007. This review clearly demonstrates the explosive growth and power of this new field of organic chemistry, which has become, in the last few years, the third methodology of asymmetric catalysis besides organometallic and enzymatic catalysis.Figure optionsView in workspaceDownload full-size imageDownload as PowerPoint slideChemInform 09/2007; 63(38):9267–9331. DOI:10.1016/j.tet.2007.06.024