Visible-Light-Driven Racemization of 1,1′-Binaphthyl-2,2′-diamine (BINAM) Derivatives

We have achieved racemization of axially chiral diamines such as 1,1′-binaphthyl-2,2′-diamine (BINAM) by utilizing a visible-light-driven single-electron oxidation. BINAM derivatives were racemized at 30–40 °C via blue-light irradiation in the presence of an Ir(dF(CF3)ppy)2(dtbpy)PF6 photocatalyst and N,N-dimethylaniline to afford racemic BINAM in 99% yield with <1% ee. Mechanistic studies demonstrated that the photocatalyst promoted the oxidation of BINAM to generate a radical cation species to facilitate racemization at low temperatures. Subsequent single-electron reduction by dimethylaniline afforded racemic BINAM. Dynamic kinetic resolution was also achieved with 80% enantioselectivity through a combination of kinetic resolution and racemization.