Direct Photoinduced Heck-Type Cyclization of Aryl Halides toward Polycyclic Indoles

In this report, we present the synthesis of 2-aryl indoles via an organo-photocatalytic pathway at room temperature. The catalysts are commercially available phenothiazine and phenoxazine, which upon deprotonation become very strong reductants and cleave a strong C-Cl bond to steer the radical process for the targeted synthesis. We proved that deprotonated phenothiazine and phenoxazine are extremely potent reductants reaching an excited-state reducing ability up to -3.41 V vs saturated calomel electrode. Photophysical studies revealed their great light-absorbing properties, which can facilitate functionalizing the indole molecules under such a mild reaction condition.