Visible-light-driven metal-free iminyl radical cyanation for the synthesis of 3-cyanoindoles

Abstract

Visible-light powered catalysis offers an efficient and environmentally friendly approach to organic synthesis. In this study, we report a photocatalytic iminyl radical cyanation (IRC) of oximes of indoles and related heterocycle in excellent yields (up to 99%) that proceeds via an organophotoredox mechanism. The reaction uses 10-phenylphenothiazine (Ph-PTZ) as an organic photocatalyst and bromotrichloromethane (BrCCl₃) as both oxidant and radical source, avoiding toxic cyanide reagents or transition metals. The methodology smoothly runs at room temperature, tolerates a wide range of functional groups, and can be scaled up to gram quantities without loss of efficiency. Experimental studies, including radical trapping, and fluorescence quenching, together with DFT calculations, support photoinduced single-electron transfer (SET) pathway involving iminyl and carbon-centered radicals. Together, these results establish a practical and sustainable approach for building nitrile-containing heterocycles using visible light as the only energy input.