Continuous-flow oxidative cyanation of primary and secondary amines using singlet oxygen

Area of Science:

• Organic Chemistry
• Photochemistry
• Synthetic Methodology

Background:

• Amines are versatile building blocks in organic synthesis.
• Oxidative transformations of amines are crucial for generating valuable nitrogen-containing compounds.
• Efficient and selective oxidation methods are continuously sought in synthetic chemistry.

Purpose of the Study:

• To develop a novel method for the oxidation of primary and secondary amines to imines using singlet oxygen.
• To synthesize α-aminonitriles via in situ trapping of the generated imines.
• To establish a new route for the synthesis of primary α-aminonitriles and subsequently amino acids.

Main Methods:

• Utilized a variable-temperature continuous-flow LED-photoreactor for singlet oxygen generation.
• Employed tetraphenylporphyrin as a photosensitizer.
• Used trimethylsilyl cyanide as an in situ imine trapping agent.

Main Results:

• Achieved rapid and quantitative oxidation of primary and secondary amines to imines.
• Synthesized α-aminonitriles in good to excellent yields.
• Developed a novel oxidative Strecker reaction at -50 °C for the first-time synthesis of primary α-aminonitriles.
• Demonstrated the synthesis of tert-leucine hydrochloride from neopentylamine, showcasing a route to racemic amino acids.

Conclusions:

• The developed method offers an atom-economic and protecting-group-free pathway for α-aminonitrile synthesis.
• This approach provides a valuable route to racemic amino acids from readily available amines.
• The use of continuous-flow photochemistry allows for efficient and controlled generation of singlet oxygen for synthetic applications.