An ew catalytic asymmetric tandem a-alkenyl addition/proton shift reaction of silyl enol ethers with ketimines was serendipitously discovered in the presence of chiral N,N'dioxide/Zn II complexes.T he proton shift preferentially proceeded instead of as ilyl shift after a-alkenyl addition of silyl enol ether to the ketimine.Awide range of b-amino silyl enol ethers were synthesized in high yields with good to excellent ee values.C ontrol experiments suggest that the Mukaiyama-Mannich reaction and tandem a-alkenyl addition/proton shift reaction are competitive reactions in the current catalytic system. The obtained b-amino silyl enol ethers were easily transformed into b-fluoroamines containing two vicinal tetrasubstituted carbon centers.
An asymmetric Meerwein-Ponndorf-Verley (MPV) reduction of glyoxylates was for the first time accomplished via an N,N'-dioxide/Y(OTf) complex with aluminium alkoxide and molecular sieves (MSs) as crucial additives. A variety of optically active α-hydroxyesters were obtained with excellent results. A possible reaction mechanism was proposed based on the experiments.
A unique chiral amine organocatalyst
with a bispidine structure
was found to be efficient for the diastereo- and enantioselective
Mannich reaction of isatin ketimines with ketones. A series of 3-substituted
3-amino-2-oxindoles bearing vicinal tertiary and quaternary chiral
stereogenic centers were obtained in excellent yields with excellent
dr and ee values. The gram-scale synthesis and transformation of the
product showed the practicability of this methodology. In addition,
a possible transition state model was proposed to explain the origin
of the stereoselectivity.
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