Synthesis of Tryptanthrins by Organocatalytic and Substrate Co-catalyzed Photochemical Condensation of Indoles and Anthranilic Acids with Visible Light and O2.

A metal-free catalytic approach to tryptanthrins has been achieved for the first time. The unique process is realized by an organocatalytic and indole and anthranilic acid substrate co-catalyzed photochemical oxidative condensation with visible light and O2. The truly environmentally friendly reaction conditions enable various reactants to participate in the process to deliver structurally diverse tryptanthrins.