Ligand-accelerated enantioselective methylene C(sp3)-H bond activation

Area of Science:

• Organic Chemistry
• Catalysis
• Asymmetric Synthesis

Background:

• Differentiating prochiral carbon-hydrogen (C-H) bonds on a single methylene carbon via asymmetric metal insertion is a significant challenge in synthetic chemistry.
• Existing methods often struggle with selectivity and efficiency, limiting the scope of C-H functionalization.

Purpose of the Study:

• To develop novel chiral ligands for asymmetric palladium insertion into prochiral C-H bonds.
• To achieve enantioselective functionalization of β-methylene C-H bonds in aliphatic amides and carboxylic acids.

Main Methods:

• Discovery of chiral acetyl-protected aminoethyl quinoline ligands.
• Application of palladium complexes with these ligands for catalytic C-H activation.
• Utilizing bidentate ligands to accelerate C-H activation and outcompete background reactions.

Main Results:

• Successful asymmetric palladium insertion into prochiral C-H bonds on a single methylene carbon center.
• Enantioselective functionalization of β-methylene C-H bonds in aliphatic amides was achieved.
• Demonstrated enantioselective β-C-H arylation of simple carboxylic acids without directing groups.

Conclusions:

• Chiral acetyl-protected aminoethyl quinoline ligands effectively enable asymmetric palladium insertion into prochiral C-H bonds.
• Ligand acceleration is crucial for achieving high enantioselectivity in C-H activation, particularly for challenging substrates.
• This methodology expands the scope of enantioselective C-H functionalization for amides and carboxylic acids.