Chiral Zinc(II)-Catalyzed Enantioselective Tandem α-Alkenyl Addition/Proton Shift Reaction of Silyl Enol Ethers with Ketimines.

A new catalytic asymmetric tandem α-alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N'-dioxide/ZnII complexes. The proton shift preferentially proceeded instead of a silyl shift after α-alkenyl addition of silyl enol ether to the ketimine. A wide range of β-amino silyl enol ethers were synthesized in high yields with good to excellent ee values. Control experiments suggest that the Mukaiyama-Mannich reaction and tandem α-alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained β-amino silyl enol ethers were easily transformed into β-fluoroamines containing two vicinal tetrasubstituted carbon centers.