Synthesis of 3,3-Disubstituted Oxindoles by Palladium-Catalyzed Asymmetric Intramolecular α-Arylation of Amides: Reaction Development and Mechanistic Studies
作者:Dmitry Katayev、Yi-Xia Jia、Akhilesh K. Sharma、Dipshikha Banerjee、Céline Besnard、Raghavan B. Sunoj、E. Peter Kündig
DOI:10.1002/chem.201301572
日期:2013.9.2
their performance is compared. One of them, L8, containing a tBu and a 1‐naphthyl group at the stereogenic centre, proved superior and was very efficient in the asymmetric synthesis of fifteen new spiro‐oxindoles and three azaspiro‐oxindoles often in high yields (up to 99 %) and enantioselectivities (up to 97 % ee; ee=enantiomeric excess). Three palladacycle intermediates resulting from the oxidative addition
掺有手性N-杂环卡宾(NHC)配体的钯配合物催化酰胺的不对称分子内α-芳基化反应,生成3,3-二取代的羟吲哚。已经进行了全面的DFT研究,以深入了解这种转变的机制。氧化添加被证明是决定速率的,还原消除是对映选择性的决定。详细介绍了七个新的NHC配体的合成,并比较了它们的性能。其中之一,L8,在立体异构中心含有一个t Bu和一个1-萘基,被证明是优越的,并且在不对称合成15个新的螺-氧杂吲哚和3个氮杂-螺氧杂吲哚中通常非常高的收率(高达99) %)和对映选择性(高达97% ee; ee =对映体过量)。分离并氧化了[Pd(NHC)]到芳基卤化物键中形成的三种palladacycle中间体,并对其结构进行了表征(X射线)。使用这些中间体作为催化剂,表明烯烃添加剂在增加周转次数和频率中起着重要的作用。