A highly enantioselective access to chiral chromanones and thiochromanones via copper-catalyzed asymmetric conjugated reduction of chromones and thiochromones.

The chromanone scaffold is a privileged structure in heterocyclic chemistry and drug discovery. A highly efficient copper-catalyzed asymmetric conjugated reduction of chromones is developed to give chiral chromanones with good yields (80-99%) and excellent ee values (94->99% ee). Particularly noteworthy is that chiral thiochromanones are also constructed using this method in 74-87% yields with 96-97% ee. The established asymmetric synthesis paves the way for their further pharmaceutical studies.