Diastereoselective cycloaddition of N-lithiated azomethine ylides to (E)-.alpha.,.beta.-unsaturated esters bearing a C2-symmetric imidazolidine chiral controller
摘要:
The 1,3-dipolar cycloaddition of N-metalated azomethine ylides to chiral (E)-3-(1,3-disubstituted 4,5-diphenylimidazolidin-2-yl)propenoates proceeded highly diastereoselectively. The previously unknown absolute configuration of optically pure 1,2-dianilino-1,2-diphenylethane was determined from the absolute configuration of the cycloadducts. What diastereotopic olefin face of the alpha,beta-unsaturated ester was attacked by the ylide was found to depend dramatically upon the nature of N substituents of the chiral controller as well as upon the bulkiness of the ester moiety of the ylide.
The asymmetric construction of quaternary carbon centers by conjugateaddition of Grignard reagents to 3-methyl- and 3-ethylcyclohexenones was realized in a maximum enantioselectivity of 80% by using a C2 symmetric chiral N-heterocyclic carbene (NHC)-copper catalyst, generated from (4S,5S)-1,3-bis(2-methoxyphenyl)-4,5-diphenyl-4,5-dihydro-1H-imidazol-3-ium tetrafluoroborate and copper(II) triflate
Synthesis of Phosphoramides for the Lewis Base-Catalyzed Allylation and Aldol Addition Reactions
作者:Scott E. Denmark、Xiping Su、Yutaka Nishigaichi、Diane M. Coe、Ken-Tsung Wong、Stephen B. D. Winter、Jun Young Choi
DOI:10.1021/jo9820723
日期:1999.3.1
Both chiral and achiral phosphoramides of diverse structure were prepared from diamines by the coupling to phosphorus(V) or phosphorus(III) reagents. Several enantiopure 1,2-diphenyl-1,2-ethanediamine analogues have been prepared by the reductive coupling of the corresponding N-silylimine with NbCl(4)(THF)(2) and subsequent resolution by the formation of diastereomeric menthyl carbamates. (S,S)-N,
Chiral Phosphoramide-Catalyzed Aldol Additions of Ketone Trichlorosilyl Enolates. Mechanistic Aspects
作者:Scott E. Denmark、Son M. Pham、Robert A. Stavenger、Xiping Su、Ken-Tsung Wong、Yutaka Nishigaichi
DOI:10.1021/jo060243v
日期:2006.5.1
mechanism of the catalytic, enantioselective addition of trichlorosilylenolates to aldehydes has been investigated. Kinetic studies using ReactIR and rapid injection NMR (RINMR) spectroscopy have confirmed the simultaneous operation of dualmechanistic pathways involving either one or two phosphoramides bound to a siliconium ion organizational center. This mechanistic dichotomy was initially postulated on
已经研究了将三氯甲硅烷基烯酸酯催化,对映选择性加成到醛的机理。使用ReactIR和快速注入NMR(RINMR)光谱进行的动力学研究已证实,涉及一个或两个与硅离子组织中心结合的磷酰胺的双机理途径的同时运行。最初基于催化剂负载量研究和非线性效应研究假定了这种机械二分法。这种二元性解释了各种类型的磷酰胺的反应性和立体选择性的差异。Arrhenius激活参数的确定表明,醛醇的添加是通过可逆的方式发生的,尽管不利的是形成了活化的复合物,并且自然丰度1313 C NMR动力学同位素效应(KIE)研究已经确定,周转限制步骤是添加羟醛。对一系列磷酰胺的彻底检查已经建立了经验结构-活性选择性关系。此外,已经研究了催化剂负载量,添加速率,溶剂和添加剂的影响,这些影响共同形成了醇醛添加的统一机理图。
New Catalytic Asymmetric Formation of Oxygen Heterocycles Bearing Nucleoside Bases at the Anomeric Carbon
作者:Barry M. Trost、Shiyan Xu、Ehesan U. Sharif
DOI:10.1021/jacs.9b06050
日期:2019.7.3
formed glyosidic bond. Herein, we report an asymmetric Pd-catalyzed synthesis of nucleoside analogs enabled by the development of a series of chiral ligands. A variety of 5-substituted pyrimidine nucleobases, ranging from 5- to 12-membered ring nucleoside analogs are generated in good yield (68% to 96%), diastereo- (> 20:1), and enantioselectivity (85% ee to 99.5% ee). These nucleoside analogs bearing an
Diastereoselective cycloaddition of N-lithiated azomethine ylides to (E)-.alpha.,.beta.-unsaturated esters bearing a C2-symmetric imidazolidine chiral controller
The 1,3-dipolar cycloaddition of N-metalated azomethine ylides to chiral (E)-3-(1,3-disubstituted 4,5-diphenylimidazolidin-2-yl)propenoates proceeded highly diastereoselectively. The previously unknown absolute configuration of optically pure 1,2-dianilino-1,2-diphenylethane was determined from the absolute configuration of the cycloadducts. What diastereotopic olefin face of the alpha,beta-unsaturated ester was attacked by the ylide was found to depend dramatically upon the nature of N substituents of the chiral controller as well as upon the bulkiness of the ester moiety of the ylide.