Structure–selectivity studies on catalysts for the phase-transfer catalysed asymmetric alkylation of glycine imine esters
摘要:
In this paper, we describe the synthesis of a series of chiral quaternary ammonium salts with core structures that are closely related to the cinchona alkaloid, cinchonine. By employing these salts as asymmetric phase-transfer agents in the benzylation of a glycine imine, an optimal catalyst structure is identified. (C) 2001 Elsevier Science Ltd. All rights reserved.
进行了系统的结构选择性研究,用手性改性的Pt / Al 2 O 3催化剂对活化的酮进行对映选择性加氢。为此,有18种改性剂,它们含有能与Pt表面形成强吸附复合物的扩展的芳族体系,以及合适的具有氨基官能团的手性基团,能够与底物的酮基相互作用(HCd,Qd,HCn,Qn在标准条件下,在AcOH和甲苯中的8种不同的活化酮上制备并测试了半合成衍生物以及合成类似物。发现底物和/或改性剂结构的相对较小的结构变化强烈影响对映选择性,并且对于所有底物都不存在“最佳”改性剂。在组合奎宁环衍生的改性剂与萘或喹啉环,获得对于所有底物的最高EES,无论是在AcOH(基板1 - 5和8中,所有承载SP 3旁边碳酮基)或甲苯(6和7,带有sp 2碳旁边的酮)。奎宁环上取代基R'的存在和性质显着影响ee(正效应和负效应)。优选芳族体系和氨基官能团的某些组合:对于喹核苷部分,喹啉和程度较小的萘是更好的匹配,而对于吡咯烷基
Asymmetric approaches to 2-hydroxymethylquinuclidine derivatives
作者:B. Lygo、J. Crosby、T. Lowdon、P.G. Wainwright
DOI:10.1016/s0040-4020(99)00050-2
日期:1999.2
Highly enantio- and diastereoselective routes to 2-hydroxymethylquinuclidines have been developed. Key steps involve the use of Sharpless dihydroxylation or Sharpless epoxidation to introduce the asymmetry with high stereocontrol, and formation of the quinuclidine ring systems via cyclisation of epoxy amines. (C) 1999 Elsevier Science Ltd. All rights reserved.