Conjugate addition of aryl nucleophiles to α,β-unsaturated cinnamic acid derivatives containing Evans type chiral auxiliaries
摘要:
Cinnamides containing oxazolidin-2-one type auxiliaries have been prepared. A novel pathway to chiral 4-aryl-6-methyl-3,4-dihydrocoumrines via the asymmetric conjugate addition of arylmagnesium bromides to these cinnamides is described. (C) 2016 Elsevier Ltd. All rights reserved.
SuperQuat 5,5-dimethyl-4-iso-propyloxazolidin-2-one as a mimic of Evans 4-tert-butyloxazolidin-2-one
作者:Steven D. Bull、Stephen G. Davies、A. Christopher Garner、Dennis Kruchinin、Min-Suk Key、Paul M. Roberts、Edward D. Savory、Andrew D. Smith、James E. Thomson
DOI:10.1039/b605244d
日期:——
The incorporation of a gem-dimethyl group at the 5-position of a chiral oxazolidinone biases the conformation of the adjacent C(4)-stereodirecting group such that the gem-dimethyl-4-iso-propyl combination mimics a C(4)-tert-butyl group, providing higher levels of stereocontrol than a simple 4-iso-propyloxazolidinone. The generality of this principle is demonstrated with applications in stereoselective enolate alkylations, kinetic resolutions, Diels–Alder cycloadditions and Pd-catalysed asymmetric acetalisation reactions.
Diastereoselective Conjugate Addition of Cyanide to α,β-Unsaturated Oxazolidinones: Enantioselective Synthesis of <i>ent</i>-Pregabalin and Baclofen
作者:Alan Armstrong、Nicola Convine、Matthew Popkin
DOI:10.1055/s-2006-941584
日期:2006.6
Conjugate addition of cyanide to chiral α,β-unsaturated oxazolidinones catalyzed by samarium(III) isopropoxide proceeds with good diastereoselectivity. The addition products can be converted into the biologically active targets ent-pregabalin and baclofen.
Free Radical-Mediated Intermolecular Conjugate Additions. Effect of the Lewis Acid, Chiral Auxiliary, and Additives on Diastereoselectivity
作者:Mukund P. Sibi、Jianguo Ji、Justin B. Sausker、Craig P. Jasperse
DOI:10.1021/ja991205e
日期:1999.8.1
We have developed a highly diastereoselective method for the conjugate addition of carbon radicals to chiral α,β-unsaturated N-enoyloxazolidinones using Bu3SnH as chain carrier and Et3B/O2 as radical initiator. Lewis acids have been screened, and Yb(OTf)3 proved to give optimized results for both chemical yield (88% for 1a and 94% for 1b) and diastereoselectivity (25:1 for 1a and 46:1 for 1b). The
Lewis acid catalyzed asymmetric halohydrin reactions of chiral α,β-unsaturated carboxylic acid derivatives with N-halosuccinimide (NXS) as the halogen source
Lewisacid catalyzed asymmetric halohydrin reactions—(halohydroxylation as well as halomethoxylation) of chiral α,β-unsaturated carboxylicacid derivatives were performed using N-halosuccinimide (NXS; X = Br, I) as the halogen source. Regio- and anti-selectivity of 100% and moderate to good diastereoselectivity with good yields were observed when Oppolzer’s sultam was used as the chiral auxiliary.
使用N-卤代琥珀酰亚胺(NXS; X = Br,I)作为卤素源,进行路易斯酸催化的手性α,β-不饱和羧酸衍生物的不对称卤代醇反应(卤代羟基化以及卤代甲氧基化)。当Oppolzer的sultam用作手性助剂时,观察到区域选择性和抗选择性为100%,中等至良好的非对映选择性,并具有良好的收率。路易斯酸中,Yb(OTf)3被发现是最好的催化剂。烯酰基和肉桂酰基底物顺利地进行了溴代醇反应,较富电子的肉桂酰基底物优选经历了碘代醇反应。但是,缺电子的肉桂酰基底物不响应此路易斯酸催化的NXS与卤代醇反应(X = Cl,Br,I)。
metathesis reactions allows for a stereoselective subsequent RuO4-catalyzed dihydroxylation. The sequence is concluded by an unusual kinetic resolution of the diastereomeric diols obtained in the oxidation reaction. As a consequence a variety of structurally diverse enantiomerically enriched diols are obtained. To the best of our knowledge the results summarized in this paper represent the first highly efficient