Visible Light‐Induced Alkylation via the Reductive Coupling of Diazoacetates With Coumarins

This work presents a synthetic method for the C 3 alkylation of coumarins via a photocatalytic coupling with diazoacetates. Mechanistic studies reveal that diazo compounds, through a proton‐coupled electron transfer process, generate highly electrophilic alkyl radicals, which subsequently add to the electron‐deficient alkene moiety of coumarins, followed by single‐electron transfer and deprotonation to afford 3‐alkylated coumarins. This protocol features good functional group tolerance, mild reaction conditions, and moderate to good yields.