Photo-induced iodination of aryl halides under very mild conditions

Aryl iodides are important precursors in synthetic chemistry that form carbon-carbon and carbon-heteroatom bonds. Most methods use transition-metal catalysts, which need to be scrupulously removed before the compounds can be used in the pharmaceutical and electronics industries, where only parts-per-million levels of transition metals are allowed. The aromatic Finkelstein iodination reaction is a powerful method of preparing valuable aryl iodides from cheap but less reactive aryl bromides and chlorides. This protocol describes a transition metal-free method for a photo-induced aromatic Finkelstein iodination reaction that is performed at room temperature (20 °C). With common aromatic bromides and sodium iodide (NaI) as the starting materials, as well as a catalytic amount of I₂ as an additive, the corresponding aromatic iodides can be synthesized in yields ranging from 56 to 93% under UV light irradiation in the absence of any metal catalysts. Various functional groups such as nitrile, ester and amino can be tolerated, which will facilitate the further functionalization of the aromatic iodides. The procedure normally requires 38-40 h to complete.