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.
electron-deficient olefins gave substituted hydrocarbazoles in up to 99% yield and 94% ee. This reaction was catalyzed by a novel chiral holmium(III) complex. Alkylation of the cycloadduct gave a tricyclic compound with four continuous chiral centers, one of which was a quaternarycarbon.
Diels-Alder Reaction of 3-Methylthiofuran and Transformation of the Cycloadducts to Substituted Cyclohexenols
作者:Ichiro Yamamoto、Koichi Narasaka
DOI:10.1246/cl.1995.1129
日期:1995.12
7-Oxabicyclo[2.2.1]hept-2-enederivatives are prepared by the Diels-Alder reaction employing 3-methylthiofuran as a diene component. A chiral titanium catalyst promotes the Diels-Alder reaction in good enantioselectivity. The cycloadducts are converted to highly functionalized cyclohexenols by treatment with silyl enol ethers and t-butyldimethylsilyl trifluoromethanesulfonate.
Lanthanide triflate-catalyzed 1,3-dipolar cycloaddition reactions of polymer-supported nitrones with alkenes for the preparation of diverse 2-isoxazoline derivatives
作者:Shū Kobayashi、Ryo Akiyama
DOI:10.1016/s0040-4039(98)02100-5
日期:1998.12
1,3-Dipolar cycloadditionreactions of polymer-supported nitrones with alkenes proceeded smoothly in the presence of a catalytic amount of a lanthanide triflate to afford the corresponding 2-isoxazolines in high yields. Diverse 2-isoxazoline derivatives were prepared based on these solid-phase reactions.
[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.
Asymmetric Michael and [2+2] cycloaddition reactions between enamines and methyl (E)-4-oxo-4-(2-oxo-1,3-oxazolidin-3-yl)-2-butenoate proceed with a chiral titanium reagent generated in situ from dichlorodiisopropoxytitanium and a tartrate-derived chiral 1,4-diol. In the presence of excess amounts of the chiral titanium reagent, good to moderate enantioselectivity is attained. The reactions are also well catalyzed even with a catalytic amount of the titanium reagent.