Enantioselective synthesis of coumarins catalyzed by an isosteviol-derived tertiary amine-squaramide catalyst.

A newly tertiary amine-squaramide organocatalyst has been successfully developed and applied into the asymmetric Michael addition of 4-hydroxycoumarin to β,γ-unsaturated α-ketoesters. The catalyst system performed well with a low catalyst loading of 1 mol% under mild reaction conditions. A series of coumarin derivatives were obtained in good to high yields (up to 97%) with high enantioselectivities (up to 96% ee).