Catalytic asymmetric indolization by a desymmetrizing [3 + 2] annulation strategy

Area of Science:

• Organic Chemistry
• Asymmetric Catalysis
• Synthetic Methodology

Background:

• Development of efficient methods for constructing complex heterocyclic scaffolds is crucial in medicinal chemistry.
• Indole derivatives are prevalent in pharmaceuticals, necessitating new synthetic routes.
• Catalytic asymmetric synthesis offers precise control over stereochemistry, particularly for creating quaternary stereocenters.

Purpose of the Study:

• To develop a novel catalytic asymmetric indolization reaction.
• To synthesize N-unprotected cyclopenta[b]indoles with an all-carbon quaternary stereocenter.
• To elucidate the reaction mechanism and identify key factors controlling stereoselectivity.

Main Methods:

• A desymmetrizing [3 + 2] annulation strategy involving ortho-amino arylboronic acids and 2,2-disubstituted cyclopentene-1,3-diones.
• Rhodium-catalyzed enantioselective addition, 5-exo-trig cyclization, and dehydration cascade.
• Quantitative Structure-Selectivity Relationship (QSSR) modeling, Density Functional Theory (DFT) calculations, non-covalent interaction analysis, and Eyring analysis.

Main Results:

• Successful development of a rhodium-catalyzed asymmetric indolization reaction.
• High yields and good enantioselectivities achieved for the synthesis of N-unprotected cyclopenta[b]indoles.
• Identification of an optimal chiral ligand through QSSR modeling that controls stereocenter formation.

Conclusions:

• The developed desymmetrizing [3 + 2] annulation strategy provides an efficient route to enantiomerically enriched cyclopenta[b]indoles.
• The study highlights the importance of ligand design in controlling stereoselectivity in catalytic asymmetric reactions.
• Mechanistic investigations provide insights into the reaction pathway and the role of the chiral ligand.