A General Approach for Preparation of Polymer-Supported Chiral Organocatalysts via Acrylic Copolymerization

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• 作者：Tor E. Kristensen ; Kristian Vestli ; Martin G. Jakobsen ; Finn K. Hansen ; Tore Hansen
• 刊名：Journal of Organic Chemistry
• 出版年：2010
• 出版时间：March 5, 2010
• 年：2010
• 卷：75
• 期：5
• 页码：1620-1629
• 全文大小：1027K
• 年卷期：v.75,no.5(March 5, 2010)
• ISSN：1520-6904

文摘

Polymer-supported chiral organocatalysts, as well as most other forms of immobilized catalysts, are traditionally prepared by a postmodification approach where modified catalyst precursors are anchored onto prefabricated polymer beads. Herein, we report an alternative and more scalable approach where polymer-supported chiral enamine and iminium organocatalysts are prepared in a bottom-up fashion where methacrylic functional monomers are prepared in an entirely nonchromatographic manner and subsequently copolymerized with suitable comonomers to give cross-linked polymer beads. All syntheses have been conducted on multigram scale for all intermediates and finished polymer products, and the catalysts have proven successful in reactions taking place in solvents spanning a wide range of solvent polarity. While polymer-supported proline and prolineamides generally demonstrated excellent results and recycling robustness in asymmetric aldol reactions of ketones and benzaldehydes, the simplest type of Jrgensen/Hayashi diarylprolinol TMS-ether showed excellent selectivity, but rather sluggish reactivity in the Enders-type asymmetric cascade. The polymer-supported version of the first-generation MacMillan imidazolidinone had a pattern of reactivity very similar to that of the monomeric catalyst, but is too unstable to allow recycling.