Copper-Catalyzed Aerobic Oxidation for the Amination of Benzoxazole Under Air

Abstract

A practical copper-catalyzed aerobic oxidation for the amination of benzoxazole with secondary amine has been discovered. This reaction has proved to be effective to a variety of amines with lower catalyst loading amount, and only oxygen in air is required to facilitate this transformation. A copper-catalyzed/amine-induced ring opening of the benzoxazole and recyclization mechanism was also proposed.

GRAPHICAL ABSTRACT

Keywords:

• Aerobic oxidation
• air
• amination
• benzoxazole
• copper

Notes

^a Reaction condition: benzoxazole (0.5 mmol), morpholine (0.6 mmol), catalyst (0.05 mmol), and 2 mL of solvent under air atmosphere for 12 h.

^b Isolated yields based on benzoxazole.

^c O₂ balloon.

^d Added 1 mmol benzoic acid.

^e Added 1 mmol acetic acid.

^f With 5% CuBr₂.

^a Reaction conditions: benzoxazole (0.5 mmol), amine (0.6 mmol), CuBr₂ (0.05 mmol), CH₃CN (2 mL), 50 °C, air.

^b Isolated yield.

^c With 2 eq amine at 50 °C for 30 h.

^d With 2 eq amine at 70 °C for 48 h.

^e With DMF as nitrogen source.

^a Reaction conditions: heteroarene (0.5 mmol), piperdine (0.6 mmol), CuBr₂ (0.05 mmol), CH₃CN (2 mL), 50 °C, air.

^b Isolated yield.

Jia-Ling Wang, Lin-Hui Wang, and Yuan-Yuan Li contributed equally to this work.