Alkyne Insertion into P–C(sp2) Bonds as a Route to Fused Phospholes: Transition-Metal-Like Reactivity at Phosphorus

While alkyne insertion into metal–carbon­(sp2) bonds is common in transition metal chemistry, direct alkyne insertions into E–C­(sp2) bonds are very rare in main group chemistry. Herein, we report a direct alkyne insertion reaction into the P–C­(aryl) bonds of tungsten-coordinated phenyl-aryl phosphenium ions, which lead to phenyl-vinyl phosphenium ions. The insertion reaction is followed by electrophilic substitution of the phosphenium ion onto the aryl group, leading to a net annulation reaction and formation of arene and heteroarene-fused phospholes. The regioselectivity of the products and computational chemistry have been used to elucidate the insertion-electrophilic substitution mechanism. This methodology has been used to synthesize known benzophosphole and phospholo­[3,2-b]­thiophene and new phospholo­[3,2-b]­pyrrole, phospholo­[2,3-b]­pyrrole, and phospholo­[2,3-b]­indole ring systems.