Synthesis of 2‑Alkenyl- and 2‑Alkynyl-benzo[b]phospholes by Using Palladium-Catalyzed Cross-Coupling Reactions

Heck, Stille, and Sonogashira reactions of 2-bromobenzo[b]phosphole P-oxide afforded a series of 2-alkenyl- and 2-alkynyl-benzo[b]phosphole P-oxides. The charge-transfer character of the new benzo[b]phosphole π-systems in the excited state is enhanced by the terminal electron-donating substituents. Furthermore, the C–Sn cross-coupling of the bromide was applied to the facile synthesis of a new Stille-coupling precursor, 2-stannylbenzo[b]phosphole.