Toward an Understanding of the High Enantioselectivity in the Osmium-Catalyzed Asymmetric Dihydroxylation. 4. Electronic Effects in Amine-Accelerated Osmylations

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• 作者：Derek W. Nelson ; Andreas Gypser ; Pui Tong Ho ; Hartmuth C. Kolb ; Teruyuki Kondo ; Hoi-Lun Kwong ; Dominic V. McGrath ; A. Erik Rubin ; Per-Ola Norrby ; Kevin P. Gable ; and K. Barry Sharpless
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：February 26, 1997
• 年：1997
• 卷：119
• 期：8
• 页码：1840 - 1858
• 全文大小：850K
• 年卷期：v.119,no.8(February 26, 1997)
• ISSN：1520-5126

文摘

Electronic effects in osmylation reactions accelerated by pyridineand quinuclidine derivatives wereinvestigated by varying the substituents on the amine ligand as well ason the alkene substrate. Ligand substituenteffects were gauged by determination of the equilibrium constants forcoordination of the amines to OsO₄, evaluationof structural properties and reduction potentials of theamine-OsO₄ complexes, and analysis of the kineticsofosmylations in the presence of the amines. Substrate substituenteffects were gauged by kinetic Hammett studiesusing several different amine/alkene combinations. NonlinearHammett relationships resulting from alkene substituenteffects were observed, and the deviation from a linear free energyrelationship was found to depend on the structure,binding capacity, and concentration of the amine. The results wereevaluated in terms of the contending "[3 +2]"and "[2 + 2]" mechanisms currently under consideration.A change in mechanism that depends on the structuraland electronic properties of both alkene and amine isproposed.