X-Ray Characterization of an Electron Donor-Acceptor Complex that Drives the Photochemical Alkylation of Indoles

A metal-free, photochemical strategy for the direct alkylation of indoles was developed. The reaction, which occurs at ambient temperature, is driven by the photochemical activity of electron donor–acceptor (EDA) complexes, generated upon association of substituted 1H-indoles with electron-accepting benzyl and phenacyl bromides. Significant mechanistic insights are provided by the X-ray single-crystal analysis of an EDA complex relevant to the photoalkylation and the determination of the quantum yield (Φ) of the process.