Visible-Light-Enabled Lanthanum-Mediated Intramolecular Epoxy-Ring Opening/Dehydrogenative Lactonization.

Area of Science:

• Organic Chemistry
• Catalysis
• Photochemistry

Background:

• Catalytic C(sp³)-H functionalization is vital for synthesizing complex organic molecules, including drugs and natural products.
• Efficient derivatization of these molecules often requires innovative catalytic strategies.

Purpose of the Study:

• To develop an efficient and practical protocol for lanthanum-catalyzed continuous epoxy-ring opening and oxidative dehydrogenative lactonization.
• To utilize visible-light irradiation for this transformation, with the lanthanum catalyst acting as both Lewis acid and photocatalyst.

Main Methods:

• Lanthanum-catalyzed reaction of epoxides with carboxylic acids under visible-light irradiation.
• Employing a balloon-oxygen atmosphere at room temperature.
• Conducting mechanistic studies and control experiments to elucidate the reaction pathway.

Main Results:

• A series of diverse isochromanones with oxygen-containing spirocyclic structural units were successfully synthesized.
• The lanthanum catalyst effectively performed both Lewis acid catalysis and photocatalysis, eliminating the need for a separate photocatalyst.
• Mechanistic studies indicated the crucial role of in situ-generated lanthanum bromide.

Conclusions:

• The developed protocol offers an efficient and practical method for synthesizing isochromanones.
• The dual role of the lanthanum catalyst simplifies the reaction setup and enhances its applicability.
• The findings provide valuable insights into lanthanum-catalyzed C-H functionalization and photocatalysis.