Asymmetric Michael additions to .alpha.,.beta.-unsaturated oxazolines. An efficient preparation of chiral .beta.,.beta.-disubstituted propionaldehydes
摘要:
A short stereoselective route to a variety of chiral, nonracemic alpha,beta-unsaturated oxazolines derived from (S)-tert-leucinol is described. Addition of organolithium reagents to this chiral oxazoline occurs in a Michael fashion, giving rise to adducts with high diastereoselectivity. Reductive cleavage of the oxazoline leaves the beta,beta-disubstituted aldehydes in > 93% ee. This process represents a significant improvement in one of the earliest asymmetric conjugate additions first reported in 1975.
Regio- and diastereoselective conjugate addition of Grignard reagents to aryl substituted α,β-unsaturated carbonyl compounds derived from Oppolzer's sultam
作者:Xiufang Cao、Fang Liu、Wenchang Lu、Gang Chen、Guang-Ao Yu、Sheng Hua Liu
DOI:10.1016/j.tet.2008.04.048
日期:2008.6
Asymmetric conjugate addition of Grignard reagents to aryl substituted α,β-unsaturatedcarbonylcompounds (1) has been achieved with great regioselectivity (>20:1) and good to excellent diastereoselectivity (de up to 98%). The nucleophilicity and stereospecific blockade of the Grignard reagents play a key role in controlling the regioselectivities and diastereoselectivities of the conjugate addition
Asymmetric Hydrogenation of Allylic Alcohols Using Ir–N,P-Complexes
作者:Jia-Qi Li、Jianguo Liu、Suppachai Krajangsri、Napasawan Chumnanvej、Thishana Singh、Pher G. Andersson
DOI:10.1021/acscatal.6b02456
日期:2016.12.2
γ-disubstituted and β,γ-disubstituted allylicalcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P–Ir-complexes on the acid-sensitive allylicalcohols. DFT ΔpKa calculations were used to explain the effect of
Dispiroketals in synthesis (Part 14): Functionalised dispiroketals as new chiral auxiliaries; highly stereoselective Michael additions to a bifunctional, C2- symmetrical chiral auxiliary
作者:Grant H. Castle、Steven V. Ley
DOI:10.1016/0040-4039(94)85340-1
日期:1994.10
A bifunctional, C2-symmetricalchiralauxiliary derived from dihydroxylateddispiroketals has been used to induce a high degree of asymmetry in Michael additions of cuprates to a variety of di-α,β-unsaturated ester systems.
Metalated chiral allylamines of type 2 (M = Li, K) are used as chiral homoenolate equivalents and allow after alkylation and acidic hydrolysis asymmetric CC bond formations to β-substituted aldehydes in enantiomeric excesses up to 67%.