Pd/Tl Bimetal-Catalyzed C3(5)–H Activation of Pyridine Derivatives Enables Access to Pyridine-Fused Benzophospholes and Their Transformation into Seven-Membered Phosphepines

A Pd/Tl bimetallic catalytic system for the efficient synthesis of pyridine-fused benzophosphole oxides via a C-H functionalization strategy has been developed. The synergistic action of the palladium catalyst and Tl(OCOCF₃)₃ enables C3(5)-H activation and intramolecular dehydrogenative coupling of 4-(diphenylphosphinoyl) pyridines, affording a series of pyridine-fused benzophosphole oxides in up to 98% yield. Remarkably, further transformations of these pyridine-fused benzophosphole oxides into seven-membered phosphepine oxides were realized via Ni/Al bimetallic catalytic system.