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。
Chiral NHC Ligands for Enantioselective Gold(I) Catalysis Under Aerobic Conditions: the Importance of Conformational Flexibility and Steric Hindrance of NHC Ligand on Reactivity
of chiral NHC−Au−Cl complexes, bearing sterically encumbered NHC ligands, has been accessed by merging anilines with commercially available chiral aminoalcohols and amines. Evaluation of the catalytic activity in enantioselective allenol cyclization has pointed out the importance of the steric hindrance and conformationalflexibility of the NHC core for reactivity. Ion metathesis between NHC−Au−Cl