Chiral Phosphoric Acid Catalyzed Enantioselective Synthesis of β-Amino-α,α-difluoro Carbonyl Compounds

A biphenol-based chiral phosphoric acid bearing a 9-anthryl group at each of the 3,3′-positions catalyzed the asymmetric Mannich-type reaction of N-Boc imine with difluoroenol silyl ethers in the presence of MS3A in THF to afford β-amino-α,α-difluoroketones in good yields and with excellent enantioselectivities. Optically pure 3,3-difluoroazetidin-2-one was readily synthesized from the Mannich-adduct.