A Brønsted Acid Catalyst for the Enantioselective Protonation Reaction
作者:Cheol Hong Cheon、Hisashi Yamamoto
DOI:10.1021/ja8041542
日期:2008.7.1
A highly reactive and robust chiral Brønstedacidcatalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Brønstedacid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Brønstedacidcatalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity.
Catalytic asymmetric hydroxymethylation of silicon enolates has been achieved. In this reaction, an aqueous solution of formaldehyde can be used to realize an easy and safe procedure, and high enantioselectivities have been obtained. This is the first example of catalytic asymmetric reactions in aqueous media with a chiral scandium complex.
Oxidation of silyl enolates was found to be smoothly catalyzed by [Cu(bpy)(BF4)2(H2O)2(bpy)]n (bpy = 4,4′-bipyridine) under molecular oxygen, and provided the corresponding α-hydroxy carbonyl compounds in high yield. The insoluble organic–inorganic hybrid polymer was readily recovered by centrifugation after the completion of reaction, and the recovered catalyst could be reused.
[reaction: see text] Asymmetric protonation of lithium enolates was examined using commercially available aminoacid derivatives as chiral proton sources. Among the aminoacid derivatives tested, Nbeta-l-aspartyl-l-phenylalanine methyl ester was found to cause significant asymmetric induction in the protonation of lithium enolates. The enantiomeric excess (up to 88% ee) of the products obtained in
strategy for the encapsulation of magneticnanobeads was developed by using the in situ self-assembly of an organic-inorganichybrid polymer. The hybrid polymer of [Cu(bpy)(BF(4))(2)(H(2)O)(2)](bpy)}(n) (bpy=4,4'-bipyridine) was constructed on the surface of amino-functionalized magnetic beads and the resulting hybrid-polymer-encapsulated beads were utilized as catalysts for the oxidation of silyl enolates