A Practical and Robust Zwitterionic Cooperative Lewis Acid/Acetate/Benzimidazolium Catalyst for Direct 1,4‐Additions

A catalyst type is disclosed allowing for exceptional efficiency in direct 1,4‐additions. The catalyst is a zwitterionic entity, in which acetate binds to CuII, which is formally negatively charged and serving as counterion for benzimidazolium. All 3 functionalities are involved in the catalytic act...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2023-03, Vol.62 (13), p.e202217519-n/a
Main Authors: Hans, Andreas C., Becker, Patrick M., Haußmann, Johanna, Suhr, Simon, Wanner, Daniel M., Lederer, Vera, Willig, Felix, Frey, Wolfgang, Sarkar, Biprajit, Kästner, Johannes, Peters, René
Format: Article
Language:English
Subjects:
Acetic acid
Asymmetric Catalysis
Benzimidazoles
Catalysis
Catalysts
Cooperative Catalysis
Copper Enolates
Hydrogen Bonds
Lewis acid
Multifunctional Catalysts
Nucleophiles
Productivity
Robustness
Stereoselectivity
Zwitterions
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Summary:A catalyst type is disclosed allowing for exceptional efficiency in direct 1,4‐additions. The catalyst is a zwitterionic entity, in which acetate binds to CuII, which is formally negatively charged and serving as counterion for benzimidazolium. All 3 functionalities are involved in the catalytic activation. For maleimides productivity was increased by a factor >300 compared to literature (TONs up to 6700). High stereoselectivity and productivity was attained for a broad range of other Michael acceptors as well. The polyfunctional catalyst is accessible in only 4 steps from N‐Ph‐benzimidazole with an overall yield of 96 % and robust during catalysis. This allowed to reuse the same catalyst multiple times with nearly constant efficiency. Mechanistic studies, in particular by DFT, give a detailed picture how the catalyst operates. The benzimidazolium unit stabilizes the coordinated enolate nucleophile and prevents that acetate/acetic acid dissociate from the catalyst. Intramolecular cooperation of CuII, coordinated acetate and a benzimidazolium unit in the catalyst periphery allows for unprecedented catalyst productivity and high stereocontrol in direct 1,4‐additions to maleimides and a number of other Michael acceptors. Next to the sophisticated activation principle, the catalyst is readily prepared and has robust reactivity. Moreover, it is shown to be reusable multiple times.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202217519