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 for organic synthesis. In this study, we report a photocatalytic iminyl radical cyanation (IRC) of oximes of indoles and related heterocycles with 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 the 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 a 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.