Ni(OTf)2-Catalyzed Michael Addition Reactions of 4-Hydroxycoumarins to α,β-Unsaturated 2-Acyl Imidazoles

An efficient Michael addition of 4-hydroxycoumarins to α,β-unsaturated 2-acyl imidazoles catalyzed by Ni(OTf)2 as a Lewis acid has been developed. A series of 4-hydroxycoumarin derivatives were obtained in excellent yields (up to 96%) with a 2 mol% catalyst loading under mild conditions. Additionally, when a chiral-at-metal rhodium complex was used as the catalyst, moderate enantioselectivity was observed (74% ee).