Medium-Ring Systems. 6.1 Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones
摘要:
A series of 3-methylenecycloalkanones with ring sizes 7-10 has been prepared and subjected to base-catalyzed isomerization. Equilibrium between these exocyclic isomers and the corresponding 3-methyl-2-cycloalkenones and 3-methyl-3-cycloalkenones was reached in the 7- and 8-membered rings. The presence of the beta-methyl shifts these equilibria toward the Delta(2) isomer in each ring relative to the unsubstituted compounds and to compounds containing electron-withdrawing groups at the beta position. In the 9- and 10-membered rings, the Delta(2) isomers were isomerized to the Delta(3) isomers only with difficulty, and the reverse process could not be accomplished under the reaction conditions utilized. The ease of interconversion of the Delta(2) and Delta(3) isomers is directly related to the thermodynamic stability of planar conjugated dienes in medium ring carbocycles.
A Practical Method for Enantioselective Synthesis of All-Carbon Quaternary Stereogenic Centers through NHC-Cu-Catalyzed Conjugate Additions of Alkyl- and Arylzinc Reagents to β-Substituted Cyclic Enones
作者:Kang-sang Lee、M. Kevin Brown、Alexander W. Hird、Amir H. Hoveyda
DOI:10.1021/ja062061o
日期:2006.6.1
Cu-catalyzed enantioselectiveconjugateadditions of alkyl- and arylzinc reagents to unactivated cyclic beta-substituted enones. Transformations are promoted in the presence of 2.5-15 mol % of a readily available chiral NHC-based Cu complex, affording the desired products bearing all-carbon quaternary stereogenic centers in 67-->98% yield and in up to 97% ee. Catalytic enantioselective reactions can
我们展示了 Cu 催化的烷基和芳基锌试剂对未活化的环状 β 取代烯酮的对映选择性共轭加成的第一个例子。在 2.5-15 mol% 的易于获得的基于手性 NHC 的 Cu 络合物的存在下促进了转化,以 67->98% 的产率和高达 97% 的 ee 提供了带有全碳四元立体中心的所需产品。催化对映选择性反应可以在台式上进行,使用未蒸馏的溶剂和市售(未进一步纯化)的铜盐。提供了机械模型,说明了对映选择性的观察水平和趋势。
Direct oxidation of tertiary allylic alcohols. A simple and effective method for alkylative carbonyl transposition
作者:William G. Dauben、Drake M. Michno
DOI:10.1021/jo00424a023
日期:1977.3
Stereochemistry of the photoinduced and Michael addition of methanol to seven- and eight-membered 2-cycloalkenones. The effect of methyl substituents
作者:Harold Hart、Bing-Lin Chen、Mark Jeffares
DOI:10.1021/jo01329a026
日期:1979.7
Asymmetric catalytic formation of quaternary carbons by iminium ion trapping of radicals
作者:John J. Murphy、David Bastida、Suva Paria、Maurizio Fagnoni、Paolo Melchiorre
DOI:10.1038/nature17438
日期:2016.4
show how the combination of photoredox and asymmetric organic catalysis enables enantioselective radical conjugate additions to β,β-disubstituted cyclic enones to obtain quaternary carbon stereocentres with high fidelity. Critical to our success was the design of a chiral organic catalyst, containing a redox-active carbazole moiety, that drives the formation of iminium ions and the stereoselective trapping
Medium-Ring Systems. 6.<sup>1</sup> Synthesis and Isomerizations of Medium-Ring 3-Methylenecycloalkanones and 3-Methylcycloalkenones
作者:Philip Eskola、Jerry A. Hirsch
DOI:10.1021/jo9705374
日期:1997.8.1
A series of 3-methylenecycloalkanones with ring sizes 7-10 has been prepared and subjected to base-catalyzed isomerization. Equilibrium between these exocyclic isomers and the corresponding 3-methyl-2-cycloalkenones and 3-methyl-3-cycloalkenones was reached in the 7- and 8-membered rings. The presence of the beta-methyl shifts these equilibria toward the Delta(2) isomer in each ring relative to the unsubstituted compounds and to compounds containing electron-withdrawing groups at the beta position. In the 9- and 10-membered rings, the Delta(2) isomers were isomerized to the Delta(3) isomers only with difficulty, and the reverse process could not be accomplished under the reaction conditions utilized. The ease of interconversion of the Delta(2) and Delta(3) isomers is directly related to the thermodynamic stability of planar conjugated dienes in medium ring carbocycles.