Pd/Tl Bimetal-Catalyzed C8-H Alkenylation of Dimethoxycoumarins.

A Pd/Tl bimetallic catalytic method for the regioselective C8-H alkenylation of dimethoxycoumarin scaffolds was developed. The synergistic effects of Tl(OCOCF3)3 and a Pd-thioether ligand catalytic system enabled electrophilic C-H bond activation, followed by Heck-type alkenylation at the C8 position of the coumarin ring, affording a series of C8-alkenylated dimethoxycoumarin derivatives in yields of up to 90%. Notably, the bimetallic catalytic system promoted electrophilic C-H activation of electron-rich coumarin scaffolds using only a catalytic amount of Tl(OCOCF3)3, enabling efficient C-H functionalization of the benzene moiety with excellent regioselectivity. This method provides a versatile and step-economical approach to highly functionalized coumarins and serves as a complementary strategy for the late-stage functionalization of coumarin-based natural products and fluorescent compounds.