Cooperative Copper/Eosin Y-Catalyzed Photochemical Oxidative Coupling Reactions of Indolines for the Synthesis of 1,5′-Biindoles

An unprecedented copper- and Eosin Y-catalyzed oxidative coupling of indolines is presented. The method provides direct access to 1,5'-biindolyls from the corresponding indolines. The reaction conditions are mild and conducted at room temperature using readily available catalysts and molecular oxygen as a terminal oxidant. Preliminary studies suggest that the reaction proceeds through a tandem oxidation/amination/oxidation process.