Photocatalytic Silylation of Aryl Alkynoates: Synthesis of Silylated Coumarins

We report a highly efficient protocol for the synthesis of 3-silyl coumarins using hydrosilanes as the silyl radical source with aryl alkynoates. Readily prepared N-aminopyridinium salts act as hydrogen atom transfer reagents for generating silyl radicals under mild conditions via photoredox catalysis. The reaction proceeds through silyl radical addition to alkyne followed by radical cascade cyclization/migration with subsequent oxidation and aromatization to give desired 3-silyl coumarins in good to excellent yields.