Photoexcited Phosphine–Acyl Iodide Complexes for the Generation of Acyl Radicals

A phosphine-catalyzed acyl iodination of tethered olefins is reported. Acid chlorides with a tethered olefin undergo an atom transfer radical cyclization reaction when subjected to magnesium iodide and catalytic triphenylphosphine under blue-light irradiation. Mechanistic studies support the activation of the acid chloride via the in situ formation of an acyl iodide allowing for the formation of an electron donor–acceptor (EDA) complex with PPh3. Density functional theory calculations support a side-on EDA complex between the aforementioned acyl iodide and triphenylphosphine. Upon irradiation, this complex generates an acyl radical, detected by EPR, and a Ph3P-I• radical. Subsequent radical cyclization and XAT generate iodinated products. The reaction tolerates a variety of functional groups and heterocycles, providing chromanone, dihydroquinolinone, thiochromanone, and dihydronaphthlenone products in moderate to high yield.