B(C 6 F 5 ) 3 /Chiral Phosphoric Acid Promoted Asymmetric C-3 gem -Difluoroalkylation of Quinoxalin-2-ones with Difluoroenoxysilanes.

The asymmetric Mannich-type reaction of quinoxalin-2-ones with difluoroenoxysilanes has been developed for the synthesis of chiral gem -difluoroalkylated quinoxalin-2-ones. The reaction worked in the presence of chiral phosphoric acid CPA 1 and B(C 6 F 5 ) 3 in THF at room temperature. The reaction exhibited a good substrate scope furnishing the products in good yields (up to 97%) with up to 96% ee .