Access to Axially Chiral Styrenes via Copper-Catalyzed Enantioselective Radical Relay Cyanophosphorylation of Alkynes

A copper-catalyzed radical relay atroposelective phosphinoylcyanation of sterically hindered aromatic alkynes with phosphine oxides and trimethylsilyl cyanide has been established. This method provides efficient access to axially chiral styrene-phosphines with high levels of chemo-, regio-, E-, and enantioselectivity. Control experiments revealed the critical role of the NHPiv group in enabling the successful atroposelective trapping of transient, highly reactive vinyl radical intermediates by a chiral Cu(II)-cyanide species.