Using the Vapourtec R-Series flow chemistry system researchers from the Max-Planck Institute for Colloids and Interfaces have shown a process were primary and secondary amines can be oxidised quantitatively using singlet oxygen to the corresponding imine. This chemistry developed by the group at Max-Planck again shows the innovative use of continuous photochemistry for efficient chemical transformations. The group has previously described the synthesis of the anti-malarial drug Artemisinin under continuous photochemical conditions using the same apparatus.
Imines are versatile, valuable building blocks in chemical synthesis which are traditionally prepared by the condensation of carbonyls and amines, this selective oxidation using singlet oxygen offers an inexpensive, atom-economic and elegant pathway.
The researchers go on to describe a variable temperature continuous flow photoreactor to obtain a-aminonitriles in excellent yields using catalytic tetraphenylporphorin (TPP) and trimethylsilyl cyaninde as an in-situ imine trap. Primary a-aminonitriles were also shown to be synthesised via an oxidative Strecker reaction for the first time to increase the diversity of un-natural amino acids.
Under these conditions the authors were able to demonstrate the oxidation of benzylic, primary and secondary amines to the corresponding secondary imines through singlet oxygen chemistry and via in-situ cyanation generate the associated a-aminonitriles in high yields.
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