α-甲锡烷基苯硫醚的异丙苯溶液在 -78 °C 下用 n-BuLi 和双(恶唑啉)-iPr 处理,随后用二苯甲酮处理,得到 99% ee 的产物。我们证实α-锂硫苄基苯硫醚的反应通过动态动力学拆分途径进行。α-锂硫苄基2-吡啶基硫醚的对映选择性反应得到的产物与苄基苯基硫醚反应得到的产物立体化学相反。我们证实该反应通过动态热力学拆分途径进行,在该途径中,与亲电子试剂的反应比非对映体复合物之间的相互转化进行得更快。
diastereomeric mixture. Each diastereomer obtained had highopticalpurity. The reaction of the α-seleno carbanion derived from the bis(phenylseleno)acetal also showed high enantioselectivity. The stereospecific elimination of the isolated diastereomers on treatment with methanesulfonyl chloride and triethylamine afforded axially chiral benzylidenecyclohexanes with high enantioselectivities up to 99% ee.
Generation of Cation Radicals from 2-Tributylstannyl-1,3-dithianes and Their Reaction with Olefins
作者:Koichi Narasaka、Tatsuo Okauchi、Noriyoshi Arai
DOI:10.1246/cl.1992.1229
日期:1992.7
Oxidation of 2-tributylstannyl-1,3-dithianes with metallic oxidants generates reactive species such as 1,3-dithian-2-yl radical and/or cation by eliminating the stannyl group. Those intermediates react with olefins to give the intermolecular addition products.
Enantioselective reaction of α-thio carbanion derived from 1-phenyl-1-(phenylthio)-1-(tributylstannyl)methane with cis-bicyclo[3.3.0]octane-3,7-dione monoethylene ketals in the presence of bis(oxazoline)s gave products with high diastereoselectivity and with high enantioselectivity. The reaction of α-seleno carbanions derived from bis(phenylseleno)arylmethanes also showed high diastereoselectivity and enantioselectivity. Deprotection and subsequent stereospecific elimination afforded axially chiral cis-arylmethylenebicyclo[3.3.0]octanes with high enantioselectivity (up to 99% ee).
Too unstable for asymmetric deprotonation, alpha-sulfenyl carbanions can undergo asymmetric substitution reactions with high stereoselectivity [Eq. (1)]. The key to the asymmetric induction is the dynamic kinetic resolution of the complex formed between the organolithium compound and a chiral ligand, the most effective of which were bisoxazoline derivatives.
Oxidative Generation of Thioalkyl Cations from 2-Tributylstannyl-1,3-dithianes and 1-(Tributylstannyl)alkyl Sulfides and Their Reactions with Olefinic Nucleophiles
作者:Koichi Narasaka、Noriyoshi Arai、Tatsuo Okauchi
DOI:10.1246/bcsj.66.2995
日期:1993.10
2-Tributylstannyl-1,3-dithianes and 1-(tributylstannyl)alkyl sulfides are oxidized with ammoniumhexanitratocerate(IV) or ferrocenium hexafluorophosphate to generate their cation radicals, which dissociate into the carbocations and tributylstannyl radical. The carbocations thus generated react with olefinic nucleophiles to afford the corresponding addition products in good yield.