Enantioselective photoredox dehalogenative protonation

Area of Science:

• Organic Chemistry
• Photocatalysis
• Asymmetric Synthesis

Background:

• Asymmetric protonation is crucial for synthesizing chiral molecules.
• Developing new methods for enantioselective synthesis remains a key challenge in organic chemistry.

Purpose of the Study:

• To report a new enantioselective photoredox dehalogenative protonation method.
• To demonstrate the synthesis of chiral ketones with high enantioselectivity.

Main Methods:

• Utilized a cooperative catalytic system with a chiral H-bonding catalyst and a dicyanopyrazine-derived chromophore (DPZ) photosensitizer.
• Employed visible light irradiation and a secondary amine as the terminal reductant.
• Applied the method to cyclic and acyclic ketones with labile α-position halogen bonds (C-F, C-Cl, C-Br).

Main Results:

• Achieved high yields for a range of cyclic and acyclic ketones.
• Obtained good to excellent enantioselectivities, up to >99% ee.
• Demonstrated the formation of chiral secondary α-halo ketones.

Conclusions:

• Established enantioselective photoredox dehalogenative protonation as a novel asymmetric protonation strategy.
• The method's success provides a pathway for constructing diverse chiral α-tertiary carbonyl compounds.
• The ready accessibility of halide precursors enhances the practicality of this approach.