Visible‐light‐mediated Synthesis of 3‐Sulfonylquinolines: Mechanistic Insights into the Photoredox Catalysis

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The visible light Ru(bpy)3Cl2 photocatalyzed synthesis of 4‐(hetero)aryl‐3‐sulfonylquinolines are reported by the reaction of N‐propargylanilines and arylsulfonyl chlorides. The diversity of the methodology for the synthesis of products with substituents on the quinoline ring, aryl/hetroaryl substituents at C4 of quinoline and aryl/alkylsulfonyl groups are reported. Detailed mechanistic studies using radical trapping experiments, cyclic voltammetry studies and fluorescence quenching studies are reported that show that contrary to expectations, the reaction proceeds through a novel major pathway involving reductive quenching of the photoexcited Ru(bpy)3Cl2 catalyst by the N‐propargylanilines as the primary photochemical step and not through oxidative quenching of the Ru(bpy)3Cl2 catalyst by the arylsulfonyl chloride to generate the arylsulfonyl radical.