From Immobilization to Catalyst Use: A Complete Continuous‐Flow Approach Towards the Use of Immobilized Organocatalysts
作者:Pedro H. R. Oliveira、Bruno M. S. Santos、Raquel A. C. Leão、Leandro S. M. Miranda、Rosane A. S. San Gil、Rodrigo O. M. A. Souza、Fernanda G. Finelli
DOI:10.1002/cctc.201901129
日期:2019.11.21
organocatalyst under a complete continuous‐flow approach, showing the impact of this method on the morphology, structure and lifetime of the organocatalyst. The first generation MacMillan's organocatalyst was prepared from L‐phenylalanine and immobilized in silica through a carbamate linkage under batch and continuous‐flowconditions. We also evaluated the performance of both batch and continuous‐flow organocatalysts
A General Approach for Preparation of Polymer-Supported Chiral Organocatalysts via Acrylic Copolymerization
作者:Tor E. Kristensen、Kristian Vestli、Martin G. Jakobsen、Finn K. Hansen、Tore Hansen
DOI:10.1021/jo902585j
日期:2010.3.5
Polymer-supported chiral organocatalysts, as well as most other forms of immobilized catalysts! arc 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 proline-amides generally demonstrated excellent results and recycling robustness in asymmetric aldol reactions or ketones and benzaldehydes, the simplest type of Jorgensen/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.