Asymmetric Continuous Oxidation Reaction Driven By Visible Light In A Microreactor

With the environment getting worse and the exhaustion of primary energy,green chemistry and sustainable development have become one of the main research contents of chemists.Scientists are more concerned about saving energy,reducing waste,decreasing production cycles and sustainable development.The micro photoreactor has the advantages of low liquid holding capacity,small floor space,high mass transfer and high heat transfer.It is also environment-friendly and sustainable and has the advantage of uniform distribution.Chiral?-hydroxy-?-dicarbonyl structural units are widely in pharmaceutical molecules.Even though there are many methods for preparing such compounds,there are still problems such as metal catalysis not green,uneven photocatalytic illumination,low atomic economy,and difficulty in mass production.Achieving this reaction with a micro photoreactor will make up the shortcomings and achieve green continuous manufacturing.Photocatalysis,asymmetric synthesis and molecular oxygen oxidation are combined with continuous reaction.Using a glass microreactor,a continuous reaction for asymmetric?-hydroxylation of?-keto ester compound is oxidized by ¹O₂ under visible light.The reaction is catalyzed by cinchona alkaloid phase transfer catalyst in gas-liquid-liquid heterogeneous system.The desired product is obtained in high yield?95%?and good enantioselectivity?87.0%ee?in 1.08 min reaction residence time in microreactor.Compared with the batch reaction,continuous reaction greatly reduces reaction residence time and maintains high stereo selectivity.This method is fast,low-energy,continuous,efficient,and has great industrial prospects.Asymmetric?-hydroxylation of?-ketoamide was studied and a series of substrates were extended to obtain seven chiral?-hydroxy-?-ketoamides?up to 90%yield,up to 88%ee?.And for the first time,the asymmetric?-hydroxylation of?-ketoamide catalyzed by cinchona base-derived phase transfer organic catalyst was realized by micro photoreactor.The reaction residence time was shortened from 8 h to 0.5 h while maintaining a high enantioselectivity?up to 86%ee?.