15, which was derived from (S)-tert-leucinol, produced (S)-18 in preference to (R)-18. A series of azolium salts were synthesized from (S)-serine esters, and the reaction conditions for the ECA reaction were optimized to produce (R)-18 with 69% ee. The best results were obtained in the case of the reaction of 4,4-dimethyl-2-cyclohexen-1-one (34) with Et2Zn catalyzed by Cu(OTf)2 in combination with azolium
Chiral alkoxy-imidazolinium salts are easily available via a five-step procedure starting from β-aminoalcohols. This new family of alkoxy-N-heterocyclic carbene (NHC) precursors is shown to be highly active in the enantioselective copper-catalysed conjugateaddition to cyclic enones. Complete conversion with lowcatalystloading and good enantiomeric excesses up to 93% were obtained at room temperature
A new approach to switching of enantioselectivity in NHC–Cu-catalyzed conjugate addition of alkylzincs to cyclic enones
作者:Masaki Okamoto、Yuko Yamamoto、Satoshi Sakaguchi
DOI:10.1039/b916103a
日期:——
Conjugate addition of Et2Zn to 2-cyclohexen-1-one catalyzed by Cu(OTf)2 combined with an azolium salt derived from (S)-leucinol produced the corresponding (S)-adduct, while the use of Cu(acac)2 in combination with the same ligand afforded the (R)-adduct as a major product.
Reversal of Stereoselectivity in the Cu-Catalyzed Conjugate Addition Reaction of Dialkylzinc to Cyclic Enone in the Presence of a Chiral Azolium Compound
Reversal of enantioselectivity in a Cu-catalyzedasymmetricconjugateaddition reaction of dialkylzinc to cyclicenone with use of the same chiral ligand was successfully achieved. The reaction of 2-cyclohexen-1-one (30) with Et2Zn catalyzed by Cu(OTf)2 in the presence of an azolium salt derived from a chiral β-amino alcohol gave (S)-3-ethylcyclohexanone (31) in good enantioselectivity. Among a series
A new C2-symmetric azolium compound for Cu-catalyzed asymmetric conjugate addition of R2Zn to cyclic enone
作者:Ayako Harano、Satoshi Sakaguchi
DOI:10.1016/j.jorganchem.2010.07.038
日期:2011.1
A new chiral N-heterocyclic carbene (NHC) ligand was designed. Thus, an efficient synthetic route to C2-symmetric bis(hydroxyamide)-functionalized benzimidazolium salts from chiral β-amino alcohols was developed. The combination of Cu(OTf)2 and the chiral azolium compound efficiently promoted the conjugate addition reaction of cyclic enone with dialkylzinc to give the corresponding adduct in good yield