Dendritic Bis(oxazoline)copper(II) Catalysts. 2.1 Synthesis, Reactivity, and Substrate Selectivity
摘要:
A series of dendritic bis(oxazoline) Ligands 1-4 were synthesized to evaluate the effects of the degree of branching of a dendritic sector on both the reactivity and selectivity of their corresponding copper(II) complex-catalyzed Diels-Alder reaction between cyclopentadiene and a crotonyl imide. Kinetic studies unveiled a two-step mechanism of the Diels-Alder reaction, in which a reversible binding of the dienophile to the copper complex was followed by a rate-determining reaction between the resulting dienophile-catalyst complex with the diene. Furthermore, two interesting features emerged: first, the formation constant of the dienophile-catalyst complex decreased gradually on going from the lower to higher generations, and secondly, while the Diels-Alder reaction rate constant remained essentially the same from the zeroth to second generation catalysts, it dropped abruptly for the third generation one. These observations were rationalized as a consequence of a folding-back of the dendritic sectors toward the catalytic unit at the third generation, so that increase in steric size impeded both the reactivity and binding profiles of the catalytic system. This behavior was reminiscent of related phenomena observed by others from solvatomatic, photophysical, and viscosity studies. In line with this reasoning, a slight but noticeable substrate selectivity was observed for the third generation catalyst, which was absence for the lower ones, in competitive kinetic studies involving two dienophiles of different steric sizes.
A Two-Carbon Homologation of Aldehydes and Ketones Using Ynamides
作者:Richard Hsung、Lingfeng You、Ziyad Al-Rashid、Ruth Figueroa、Sunil Ghosh、Gang Li、Ting Lu
DOI:10.1055/s-2007-984513
日期:2007.7
Reactions of ynamides with Lewis acid activated -aldehydes, enals, or ketones in the formation of acrylic amides are described here. The overall process is an equivalent of a two-carbonhomologation of aldehydes or ketones and is selective for the E-isomer.
在此描述了炔酰胺与路易斯酸活化的醛、烯醛或酮在丙烯酰胺形成中的反应。整个过程相当于醛或酮的双碳同系化,并且对 E 异构体具有选择性。
Construction of a new asymmetric reaction site: asymmetric 1,4-addition of thiol using pentagonal bipyramidal Hf(salen) complex as catalyst
Pentagonal bipyramidal Hf(salen) complex I was found to serve as a catalyst for 1,4-addition reaction of thiol to N-(2alkenoyl)-2-oxazolidinones. (C) 2004 Elsevier Ltd. All rights reserved.
One-pot dehydrogenation of carboxylic acid derivatives to α,β-unsaturated carbonyl compounds under mild conditions
作者:Jun-ichi Matsuo、Yayoi Aizawa
DOI:10.1016/j.tetlet.2004.11.106
日期:2005.1
Carboxylic acidderivatives such as N-acyl-2-oxazolidones, δ-lactones, and δ-lactams were smoothly dehydrogenated to the corresponding α,β-unsaturatedcarbonylcompounds in one-pot manner at −78 °C just by treating their lithium enolates with N-tert-butylbenzenesulfinimidoyl chloride.
Dendritic Bis(oxazoline)copper(II) Catalysts. 2.<sup>1</sup> Synthesis, Reactivity, and Substrate Selectivity
作者:Hak-Fun Chow、Chi Ching Mak
DOI:10.1021/jo970383s
日期:1997.7.1
A series of dendritic bis(oxazoline) Ligands 1-4 were synthesized to evaluate the effects of the degree of branching of a dendritic sector on both the reactivity and selectivity of their corresponding copper(II) complex-catalyzed Diels-Alder reaction between cyclopentadiene and a crotonyl imide. Kinetic studies unveiled a two-step mechanism of the Diels-Alder reaction, in which a reversible binding of the dienophile to the copper complex was followed by a rate-determining reaction between the resulting dienophile-catalyst complex with the diene. Furthermore, two interesting features emerged: first, the formation constant of the dienophile-catalyst complex decreased gradually on going from the lower to higher generations, and secondly, while the Diels-Alder reaction rate constant remained essentially the same from the zeroth to second generation catalysts, it dropped abruptly for the third generation one. These observations were rationalized as a consequence of a folding-back of the dendritic sectors toward the catalytic unit at the third generation, so that increase in steric size impeded both the reactivity and binding profiles of the catalytic system. This behavior was reminiscent of related phenomena observed by others from solvatomatic, photophysical, and viscosity studies. In line with this reasoning, a slight but noticeable substrate selectivity was observed for the third generation catalyst, which was absence for the lower ones, in competitive kinetic studies involving two dienophiles of different steric sizes.