Visible-light driven acetoxylation and dioxygenation of indoles via electron donor-acceptor complexes.

A photoresponsive electron donor-acceptor (EDA) complex, formed by indole and hypervalent iodine such as diacetoxyiodobenzene (DAIB/PIDA, etc. ), was detectable through absorption and emission spectroscopy. Irradiation of the EDA complex with visible light triggered photoinduced single electron transfer (SET) processes that were synthetically useful for the catalyst-free, regioselective acetylation of indoles. The photocatalytic reaction with excess DAIB was also used for the synthesis of isatins. The synthetic protocols were tolerant of a wide variety of substituents on the indole ring, including N -substitutions. DFT and TD-DFT studies were performed to model the excited states of the EDA complex and validate the photoinduced SET mechanism.