Chiral Macrocycle-Enabled Counteranion Trapping for Boosting Highly Efficient and Enantioselective Catalysis

Area of Science:

• Organic Chemistry
• Catalysis
• Supramolecular Chemistry

Background:

• Macrocycles are effective in catalysis, particularly crown ethers for cation binding.
• Developing new strategies for anion binding in catalysis is crucial for expanding synthetic methodologies.

Purpose of the Study:

• To present a novel macrocycle-enabled counteranion trapping strategy for enhanced catalysis.
• To design and synthesize bis-diarylthiourea macrocycles for enantioselective reactions.
• To investigate the catalytic efficiency and stereocontrol in Friedel-Crafts reactions.

Main Methods:

• Synthesis of bis-diarylthiourea macrocycles incorporating BINOL moieties.
• Evaluation of catalytic activity in the Friedel-Crafts reaction of indoles with imines.
• Analysis of enantioselectivity using chiral chromatography.

Main Results:

• The synthesized macrocycles exhibit strong binding affinities for disulfonate anions.
• A catalytic system using 1 mol% macrocycle and 1 mol% ethanedisulfonic acid achieved high conversion and up to 99% enantiomeric excess (ee).
• Neither the macrocycle nor the acid alone showed significant catalytic activity.

Conclusions:

• The macrocycle-enabled counteranion trapping strategy is highly effective for boosting catalytic efficiency and enantioselectivity.
• Complexation-induced acidity enhancement and tight ion-pairing within the macrocyclic cavity are key to the observed high performance.
• This approach offers a powerful new tool for asymmetric catalysis.