Photo‐Induced 3‐Alkylation of Coumarins with Alkyl halides

A method for the direct 3‐alkylation of coumarins utilizing alkyl halides as the alkylating agents has been achieved. This versatile reaction is compatible with a range of alkyl halides, including activated alkyl bromides, perfluoroalkyl iodides, and unactivated alkyl iodides. We propose a mechanism involving photoinduced electron transfer between alkyl halides and coumarins in the first singlet excited (S1) state, which generates alkyl radicals essential for the 3‐alkylation process.