Enantioselective Intermolecular Photocycloaddition of Indoles.

Area of Science:

• Organic Chemistry
• Photochemistry
• Asymmetric Synthesis

Background:

• Photocycloaddition (PCA) is a known method for synthesizing cyclobutane-fused heterocycles from heteroarenes.
• Achieving high enantioselectivity in these reactions remains a significant challenge in synthetic chemistry.

Purpose of the Study:

• To develop an efficient and enantioselective intermolecular [2+2] cycloaddition of indoles with alkenes and aryl allenes.
• To utilize visible light irradiation for driving the cycloaddition reaction.
• To establish a versatile route for enantioenriched cyclobutane-fused heterocycles.

Main Methods:

• Employed a chiral oxazaborolidinium ion (COBI) catalyst to coordinate with indole substrates.
• Utilized visible light irradiation to initiate the photocycloaddition reaction.
• Investigated the radical addition to alkenes as the enantio-determining step, followed by radical recombination.

Main Results:

• Successfully achieved efficient and enantioselective intermolecular [2+2] cycloaddition of indoles.
• Demonstrated broad substrate compatibility and functional group tolerance.
• Produced enantioenriched cyclobutane-fused heterocycles with high efficiency.

Conclusions:

• The developed COBI-catalyzed photocycloaddition provides a novel and versatile strategy for synthesizing valuable cyclobutane-fused heterocycles.
• This method overcomes previous limitations in achieving high enantioselectivity for this class of compounds.
• The strategy offers a significant advancement in asymmetric synthesis using visible light.