Stereoselective Synthesis Of Trisubstituted Epoxides Via Cobalt Catalysis

Epoxides are common structural units found in a variety of bioactive natural products and pharmaceutical agents.In addition,these compounds are important building scaffolds for the synthesis of various organic compounds due to their inherent ring strain.Therefore,the efficient synthesis of such compounds is of great significance.In recent years,transition-metal-catalyzed construction of epoxides offers an atom-and step-economical route from readily available aldehydes and diazocarbonyl compounds,while nitrogen is generated as the sole byproduct.Then rhodium,silver and iron catalysts have been extensively used in such transformations to afford the trisubstituted epoxides with cis selectivity.Herein we report that the cobalt catalyst could promote the epoxide synthesis in ligand-free conditions with excellent trans selectivity,which is different from the previous reports.The product could be generated in moderate to good yields with excellent diasteroselectivity.The reaction is applicable to aryl,heteroaryl and aliphatic aldehydes.Preliminary mechanism studies show the present catalytic system features a distinctively mechanism from other transition-metal catalyzed epoxides synthesis,which does not involve the metal carbine and ylide intermediates.