Enantioselective Lewis Acid-Catalyzed Mukaiyama−Michael Reactions of Acyclic Enones. Catalysis by <i>a</i><i>llo</i>-Threonine-Derived Oxazaborolidinones
作者:Xiaowei Wang、Shinya Adachi、Hiroyoshi Iwai、Hiroshi Takatsuki、Katsuhiro Fujita、Mikako Kubo、Akira Oku、Toshiro Harada
DOI:10.1021/jo035379x
日期:2003.12.1
Mukaiyama-Michael reaction of acyclic enones with a trimethylsilyl ketene S,O-acetal in high enantioselectivity. A range of alkenyl methyl ketones is successfully employed as Michael acceptors affording ee values of 85-90% by using 10 mol % of the catalyst. The use of 2,6-diisopropylphenol and tert-butyl methyl ether as additives is found to be essential to achieve high enantioselectivity in these reactions.
异苏氨酸衍生的O-芳酰基-B-苯基-N-甲苯磺酰基-1,3,2-氧杂硼硼烷-5-酮1g,n催化无环烯酮与三甲基甲硅烷基乙烯酮S,O-乙缩醛的不对称Mukaiyama-Michael反应具有高对映选择性。通过使用10 mol%的催化剂,一系列烯基甲基酮被成功用作Michael受体,ee值为85-90%。已发现使用2,6-二异丙基苯酚和叔丁基甲基醚作为添加剂对于在这些反应中实现高对映选择性是必不可少的。根据阻滞Si(+)催化的外消旋途径来讨论添加剂的作用,这会严重恶化不对称Mukaiyama-Michael反应的对映选择性。基于催化剂结构与对映选择性之间的相关性,提出了一种不对称诱导的工作模型。