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Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
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Catalytic Asymmetric Cyclopropanations with Nonstabilized Carbenes
Kristen E Berger1, Raymond J Martinez1, Jianhan Zhou1
1Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States.
Journal of the American Chemical Society
|April 22, 2023
Summary
This study introduces a new method for synthesizing chiral cyclopropanes using gem-dichloroalkanes as precursors to nonstabilized carbenes. This approach offers a safer alternative to traditional diazoalkane methods, achieving high enantioselectivity in asymmetric cyclopropanation reactions.
Area of Science:
- Organic Chemistry
- Asymmetric Synthesis
- Catalysis
Background:
- Chiral cyclopropanes are vital structural motifs in pharmaceuticals, agrochemicals, and materials science.
- Current methods for synthesizing chiral cyclopropanes often rely on catalytic additions of diazoalkanes to alkenes.
- A significant limitation of diazoalkane methods is the requirement for stabilizing substituents for safe handling on preparative scales.
Purpose of the Study:
- To develop a novel and safer method for the asymmetric cyclopropanation of alkenes.
- To utilize gem-dichloroalkanes as precursors for nonstabilized carbenes in cyclopropanation reactions.
- To achieve high enantioselectivity in the synthesis of chiral cyclopropanes.
Main Methods:
- Employing gem-dichloroalkanes as carbene precursors.
- Utilizing a cobalt catalyst for the asymmetric cyclopropanation reaction.
- Investigating the reaction mechanism, including the proposed formation of a cationic carbenoid species.
Main Results:
- Demonstrated the successful use of gem-dichloroalkanes for generating nonstabilized carbenes.
- Achieved high levels of enantioselectivity across various alkene substrates, including monosubstituted, 1,1-disubstituted, and internal alkenes.
- Confirmed compatibility with alkyl-substituted carbenes, which are prone to side reactions like 1,2-hydride shifts.
Conclusions:
- Established a novel and efficient route to chiral cyclopropanes from gem-dichloroalkanes.
- Overcame the safety limitations associated with traditional diazoalkane precursors.
- Provided a versatile method for asymmetric cyclopropanation with broad substrate scope and high enantiocontrol.
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