Organocatalyzed Enantioselective Protonation of Silyl Enol Ethers: Scope, Limitations, and Application to the Preparation of Enantioenriched Homoisoflavones
In the present work, enantioselective protonation of silylenolethers is reported by means of a variety of chiral nitrogen bases as catalysts, mainly derived from cinchonaalkaloids, in the presence of various protic nucleophiles as proton source. A detailed study of the most relevant reaction parameters is disclosed allowing high enantioselectivities of up to 92% ee with excellent yields to be achieved
Reaction of lithium enolates of 2-arylcycloalkanones 2 with (R,R)-aminoborane 1, prepared from (1R,2R)-1,2-diaminocyclohexane 4 and PhBCl2, gives the corresponding optically active ketones 3 with up to 93% ee; this is the first example of enantioselective protonation using a metal-containing chiral proton source.
[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
Asymmetric Protonation of Ketone Enolates Using Chiral <i>β</i>-Hydroxyethers: Acidity-Tuned Enantioselectivity
作者:B. Moon Kim、Hyunwoo Kim、Woosung Kim、Keun Young Im、Jin Kyoon Park
DOI:10.1021/jo0498258
日期:2004.7.1
New chiral hydroxyethers 1a−f were prepared for asymmetric protonation of achiral enolates prepared from prochiral ketones. The enantioselectivity of protonation was highly dependent upon the acidity of the chiral alcohols, the highest enantioselectivity (90% ee) being achieved with 3,5-dichloro-substituted β-hydroxyether 1c. A salt-free enolate generated from trimethylsilyl enol ether 4 provided product