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

Area of Science:

• Organic Chemistry
• Photocatalysis
• Asymmetric Synthesis

Background:

• Axially chiral diamines are crucial building blocks in asymmetric synthesis.
• Racemization of chiral compounds is essential for dynamic kinetic resolution processes.
• Developing efficient and mild racemization methods is a key challenge in organic chemistry.

Purpose of the Study:

• To develop a novel visible-light-driven method for the racemization of axially chiral diamines.
• To investigate the mechanism of photocatalytic racemization.
• To achieve dynamic kinetic resolution of chiral diamines via combined racemization and resolution.

Main Methods:

• Visible-light irradiation using blue light.
• Employing an iridium-based photocatalyst, Ir(dF(CF3)ppy)2(dtbpy)PF6.
• Utilizing N,N-dimethylaniline as a single-electron reductant.
• Low-temperature reaction conditions (30-40 °C).

Main Results:

• Efficient racemization of 1,1'-binaphthyl-2,2'-diamine (BINAM) derivatives achieved.
• Racemic BINAM obtained in 99% yield with <1% enantiomeric excess (ee).
• Mechanistic studies confirmed a single-electron oxidation pathway via a radical cation intermediate.
• Dynamic kinetic resolution achieved with 80% enantioselectivity.

Conclusions:

• Visible-light photocatalysis offers a mild and efficient route for racemizing axially chiral diamines.
• The developed method facilitates low-temperature racemization and enables high-enantioselectivity dynamic kinetic resolution.
• This approach provides a valuable tool for accessing enantiomerically enriched compounds from racemic precursors.