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
step is the intramolecular conjugate addition of a phenolic nucleophile on a α,β-unsaturated ester catalyzed by Cinchonaalkaloids. The high ee’s obtained with cinchonine and its derivatives have been rationalized by ab initio quantum chemistry calculations of transition state structures.