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
Enantioselective Spirocyclopropanation of <i>para</i>-Quinone Methides Using Ammonium Ylides
作者:Lukas Roiser、Mario Waser
DOI:10.1021/acs.orglett.7b00869
日期:2017.5.5
The use of Cinchonaalkaloid-based chiral ammonium ylides allows for the first highlyenantioselective and broadly applicable spirocyclopropanation reactions of para-quinone methides. This strategy provides a straightforward protocol toward the chiral spiro[2.5]octa-4,7-dien-6-one skeleton, which is a frequently found structural motif in important biologically active molecules.
Catalytic Asymmetric Bromine-Lithium Exchange: A New Tool to Build Axial Chirality
作者:Quentin Perron、Alexandre Alexakis
DOI:10.1002/adsc.201000517
日期:2010.10.4
We present here the first catalytic desymmetrization of the 2,2′,6,6′-tetrabromobiphenyl 1 and analogues, by a bromine-lithiumexchange catalyzed by either diamines or diether derivatives (0.5 equiv.), yielding axiallychiral compounds in high yield (up to 89%) and high enantioselectivity (up to 82%).
Designing Fluorinated Cinchona Alkaloids for Enantioselective Catalysis: Controlling Internal Rotation by a Fluorine-Ammonium Ion gauche Effect (φNCCF)
The C9 position of cinchonaalkaloids functions as a molecular hinge, with internalrotations around the C8C9 (τ1) and C9C4′ (τ2) bonds giving rise to four low energy conformers (1; anti‐closed, anti‐open, syn‐closed, and syn‐open). By substituting the C9 carbinol centre by a configurationally defined fluorine substituent, a fluorine‐ammonium iongaucheeffect (σC−H→σC−F*; Fδ−⋅⋅⋅N+) encodes for two
The reaction of cinchonidine (cinchonine)-derived ammonium salts with nitroolefins in the presence of Cs2CO3 to afford optically active isoxazolineN-oxides with excellent ee and high de values has been developed.