Asymmetric [2 + 2] cycloaddition reaction catalyzed by a chiral titanium reagent
摘要:
In the presence of certain Lewis acids, alkenes containing an alkylthio group (for example, ketene dithioacetals, alkenyl sulfides, alkynyl sulfides, and allenyl sulfides) react with electron deficient olefins to give the corresponding cyclobutane, cyclobutene, or methylene cyclobutane derivatives. By employing a chiral titanium catalyst generated in situ from dichlorodiisopropoxytitanium and a tartrate-derived chiral diol, the [2 + 2] cycloaddition reaction proceeds with high enantioselectivity.
Asymmetric [2 + 2] cycloaddition reaction catalyzed by a chiral titanium reagent
摘要:
In the presence of certain Lewis acids, alkenes containing an alkylthio group (for example, ketene dithioacetals, alkenyl sulfides, alkynyl sulfides, and allenyl sulfides) react with electron deficient olefins to give the corresponding cyclobutane, cyclobutene, or methylene cyclobutane derivatives. By employing a chiral titanium catalyst generated in situ from dichlorodiisopropoxytitanium and a tartrate-derived chiral diol, the [2 + 2] cycloaddition reaction proceeds with high enantioselectivity.
Ene reaction proceeds between 1-alkyl-1,2-propadienyl sulfides and aldehydes in the presence of BF3·OEt2 to afford 1,3-dienes possessing an alkylthio group. On the other hand, the reactions of 1-silyl-1,2-propadienyl sulfides with aldehydes or their dimethylacetals give aldol-type addition products, α-methylene acylsilanes.
[2+2] Cycloaddition Reaction between Allenyl Sulfides and Electron Deficient Olefins Promoted by Lewis Acids
作者:Yujiro Hayashi、Shigeo Niihata、Koichi Narasaka
DOI:10.1246/cl.1990.2091
日期:1990.11
Methylenecyclobutane derivatives are prepared by the Lewis acid promoted [2+2] cycloaddition reactions of 1-substituted-1-methylthio-1,2-propadienes and electron deficient olefms. The asymmetric [2+2] cycloaddition of the allenyl sulfides also proceeds in high enantioselectivity by the use of a chiral titanium reagent.
and olefinic nucleophiles containing an alkylthio substituent. Ketene dithioacetal or 2-(methylthio)allylsilane reacts with Schiff’s bases in the presence of trifluoromethanesulfonic acid to afford β-amino acid equivalents or homoallylic amines, respectively. On the other hand, ene reaction proceeds between 1-alkyl-1,2-propadienyl sulfides and Schiff’s bases by treatment with AlCl3, giving 1,3-dienes
Enereaction proceeds between α-alkylallenyl sulfides and enophiles such as aldehydes and Schiffs bases in the presence of Lewisacid to afford various 1,3-dienes.