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Bifunctional asymmetric catalysis: cooperative Lewis acid/base systems.
Daniel H Paull1, Ciby J Abraham, Michael T Scerba
1Department of Chemistry, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA.
Accounts of Chemical Research
|April 12, 2008
Summary
This study highlights bifunctional catalysts that combine Lewis acids and bases for efficient asymmetric synthesis. These systems achieve high enantioselectivity in cycloaddition reactions by activating both reaction partners simultaneously.
Area of Science:
- Organic Chemistry
- Catalysis
- Asymmetric Synthesis
Background:
- Growing emphasis on multifunctional catalytic systems to mimic enzyme efficiency.
- Multifunctional catalysts enhance reaction efficiency and selectivity.
- Bifunctional catalysis enables simultaneous activation of electrophilic and nucleophilic partners.
Purpose of the Study:
- Illustrate the importance of bifunctional catalytic methods.
- Focus on cooperative action of Lewis acidic and Lewis basic catalysts.
- Present novel bifunctional methods for enantioselective cycloaddition reactions.
Main Methods:
- Combining achiral Lewis acids with chiral cinchona alkaloid nucleophiles (e.g., benzoylquinine).
- Utilizing Lewis acids to coordinate and activate electrophiles.
- Catalyzing enantioselective cycloaddition reactions between ketene enolates and electrophiles.
Main Results:
- Developed three distinct bifunctional methods.
- Achieved highly enantioselective cycloaddition reactions.
- Lewis acids increased reaction rates and yields without compromising enantioselectivity.
Conclusions:
- Bifunctional catalysis is crucial for efficient asymmetric synthesis.
- Cooperative activation by Lewis acids and bases enhances catalytic performance.
- Chiral cinchona alkaloid-based systems offer a powerful approach for enantioselective transformations.
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