Visible-Light-Driven Racemization of 1,1'-Binaphthyl-2,2'-diamine (BINAM) Derivatives
Tatsuhiro Uchikura1, Mikoto Sato1, Yuki Kanno1
1Department of Chemistry, Faculty of Science, Gakushuin University, Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
Abstract:
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.
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