Visible light-promoted enantioselective aerobic oxidation of pyrazolones by phase transfer catalysis

Abstract

An efficient and enantioselective aerobic oxidation of 4-substituted pyrazolones has been developed by phase transfer catalysis. Using visible light as the driving force and O2 (in air) as the oxidant, broad scopes (38 examples) of pyrazolones bearing an oxygen-attached carbon stereocenter at C-4 position were obtained in high yields (up to 98%) and excellent enantioselectivities (up to 93% ee) under mid conditions. The ready availability of catalyst, ease of operation, and low-cost and eco-friendly nature highlighted the practical utility of this visible light-promoted enantioselective aerobic oxidation.

Keywords

• Aerobic oxidation
• Pyrazolone
• Visible light
• Phase transfer catalysis
• Cinchona alkaloid