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

Abstract

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.