Visible Light‐Induced Metal‐free Arylation of Coumarin‐3‐carboxylates with Arylboronic Acids

The present work reports a novel methodology for the selective arylation of coumarin‐3‐carboxylates with arylboronic acids via a photochemical route, marking the first‐ever attempt for the direct alkenyl C‐H arylation using rose bengal as a photocatalyst, which is a readily available and cost‐effective alternative to transition metal catalysis. The reaction proceeds smoothly in MeOH/H2O solvent media in the presence of radical initiator affording the arylated products in good yields (60‐80%). The reaction parameters such as visible light, radical initiator, oxidant, anhydrous solvent, and inert atmosphere play a crucial role for the success of this methodology. The substituents present on the substrate show a significant effect on the conversion. This study provides a valuable contribution to the field of organic synthesis offering a new and efficient approach to the arylation of coumarin‐3‐carboxylic acid esters with a broad substrate scope and high functional group tolerance. It is a versatile method and provides a direct access to biologically relevant 4‐arylcoumarin‐3‐carboxylates.