Zhou Jian, Ye Meng-Chun, Huang Zheng-Zheng, Tang Yong
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China.
J Org Chem. 2004 Feb 20;69(4):1309-20. doi: 10.1021/jo035552p.
Pseudo-C(3)-symmetric trisoxazoline copper(II) complexes prove to be excellent catalysts in the Friedel-Crafts alkylation of indoles with alkylidene malonates. The absolute stereochemistry of this reaction is shown to be dependent on the solvent. Reactions in isobutyl alcohol afford the Friedel-Crafts alkylation adducts in excellent yields and with up to +98% ee. In 1,1,2,2-tetrachloroethane (TTCE), however, the opposite enantiomers of the products are obtained in good yields with up to -89% ee. Water tolerance of chiral catalyst trisoxazoline 2a/Cu(OTf)(2) is examined, and it is found that the addition of up to 200 equiv of water relative to catalyst in isobutyl alcohol has almost no effect on enantioselectivity but slows down the reaction. The reaction scope is studied as well. The roles of alcohol as the solvent to accelerate the reaction are discussed. The stereochemical models of asymmetric induction for reactions both in isobutyl alcohol and in TTCE are also developed.
伪C(3)-对称三恶唑啉铜(II)配合物被证明是吲哚与亚烷基丙二酸酯进行傅克烷基化反应的优秀催化剂。该反应的绝对立体化学显示取决于溶剂。在异丁醇中反应可得到高产率的傅克烷基化加合物，对映体过量高达+98%。然而，在1,1,2,2-四氯乙烷（TTCE）中，可得到产率良好、对映体过量高达-89%的产物的相反对映体。对手性催化剂三恶唑啉2a/Cu(OTf)₂的耐水性进行了研究，发现在异丁醇中相对于催化剂加入高达200当量的水对映选择性几乎没有影响，但会使反应减慢。还研究了反应范围。讨论了醇作为加速反应的溶剂的作用。还建立了在异丁醇和TTCE中反应的不对称诱导立体化学模型。
