Takahiko Akiyama

Abstract The hydrosilylation of alkenes is one of the most important methods for the synthesis of organosilicon compounds. In addition to the platinum‐catalyzed hydrosilylation, silyl radical addition reactions are notable as economic reactions. An efficient and widely applicable silyl radical addition reaction was developed by using 2‐silylated dihydroquinazolinone derivatives under photocatalytic conditions. Electron‐deficient alkenes and styrene derivatives underwent hydrosilylation to give addition products in good to high yields. Mechanistic studies indicated that the photocatalyst functioned not as a photoredox catalyst but as an energy transfer catalyst. DFT calculations clarified that the triplet excited state of 2‐silylated dihydroquinazolinone derivatives released a silyl radical through the homolytic cleavage of a carbon‐silicon bond, and this was followed by the hydrogen atom transfer pathway, not the redox pathway.