Diels-Alder reactions in room-temperature ionic liquids

doi:10.1016/S0040-4039(98)02415-0

Tetrahedron Letters

Volume 40, Issue 4, 22 January 1999, Pages 793-796

https://doi.org/10.1016/S0040-4039(98)02415-0 Get rights and content

Abstract

The Diels-Alder cycloaddition reaction between methyl acrylate and cyclopentadiene has been investigated in a number of air and moisture stable ionic liquids. The endo/exo ratio of the reaction has been used as an initial probe of the nature of the solvents.

Room-temperature ionic liquids are used as solvents for regioselective Diels-Alder reactions.

References (10)

J. Howarth et al.
Tet. Lett.
(1997)
D.A. Jaeger et al.
Tet. Lett.
(1989)
R. Breslow et al.
Tet. Lett.
(1983)
A.A.-Z. Samii et al.
Tetrahedron
(1985)
J.S. Wilkes et al.
Inorg. Chem.
(1982)

There are more references available in the full text version of this article.

Cited by (444)

Electrically and thermally healable nanocomposites via one-step Diels-Alder reaction on carbon nanotubes
2023, Polymer
Carbon nanotubes (CNTs) were directly employed as reactive fillers in furan-pendant polyketones via the Diels-Alder (DA) reaction. CNTs and furan groups function as dienophile and diene, respectively, forming a reversible crosslinking network. Here, pristine CNTs not only serve as crosslinking agents, but also improve the thermal and electrical conductivity. The DA covalent linkage was confirmed by IR, TGA, DSC, elemental analysis and dispersion tests. This one-step approach offers a facile route to synthesize reversibly crosslinked thermoset polymer nanocomposites. The rigidity of the nanocomposites could be controlled through the number of furan groups in order to achieve distinct properties. The nanocomposites demonstrated dynamic temperature-dependent behavior due to the retro Diels-Alder reaction. Cyclic tests via rheology showed good reversibility below 120 °C. However, an irreversible increase of modulus was observed at higher temperatures, which is possibly attributed to a side reaction. At filler loadings above 5%, both electrical and thermal self-healing tests showed good results. The Diels-Alder reaction between CNTs and furan-pendant polymers opens up a new possibility of directly employing fillers in the polymer matrix without any prior modifications. It is also possible to use other fillers with diene/dienophile properties in future reversible polymer nanocomposites.
Piperidinium borate catalyzed Knoevenagel condensation of carbonyl compounds with active methylenes
2023, Tetrahedron Letters
A piperidinium borate, an organic conjugate base as a catalyst under mild conditions, effectively promotes Knoevenagel condensation between aromatic, heterocyclic, α, β unsaturated aldehydes and aliphatic, cyclic ketones with active methylenes. Piperidinium borate can be easily prepared from widely available boric acid and piperidine. The present method showed the advantages of mild reaction conditions, wide and easy availability of starting materials, and higher product yields. In addition, all the products were separated simply by filtering and washing with water. The intermediate of AMG 837, a new GPR40 agonist, was synthesized using the similar reaction conditions used in this protocol. Furthermore, the recyclability and reusability of the catalyst are also excellent.
Synthesis of environmentally benign new ionic liquids for the preparation of 2-aryl/heteroaryl benzimidazoles/benzoxazoles under ultrasonication
2022, Sustainable Chemistry and Pharmacy
Ionic liquids (ILs) possess a broad spectrum and cutting-edge impact on promising and sustainable research works due to their utilization in academic as well as industrial applications. These are regarded as notable catalysts/solvents due to their distinct physical, thermal and chemical properties. Among the different ILs existing, imidazolinium salts are quite interesting because of their convenient preparation and widespread applications in organic catalysis. By keeping in mind aforesaid, we have synthesized a series of ionic liquids; symmetrical/unsymmetrical 1,3-dialkyl imidazolium/benzimidazolium salts from imidazole/benzimidazole with alkyl chlorides/bromides. Further, ILs with other counter-anions such as tetrafluoroborate (BF₄⁻) and hexafluorophosphate (PF₆⁻) in benzimidazolium group were developed by the reaction of N, N′-disubstituted o-phenylenediamine, triethyl orthoformate and ammonium chloride/tetrafluoroborate/ammonium hexafluorophosphate. By these ionic liquids, a series of substituted 1-alkyl-2-aryl-1H-benzo[d]imidazole/2-arylbenzo[d]oxazoles were prepared from the reaction between N-substituted-1,2-phenyldiamine/o-aminophenol and aroyl chlorides without adding any acid catalyst and organic solvents. The current work discloses, when increase the length of the alkyl chain on the imidazolinium ionic liquids correspondingly the product yields were raised, similarly, the different anions offered a different rate of reactivity as BF₄⁻ ∼ Br⁻ > Cl⁻ > PF₆⁻. Further, we extended our studies to conduct the same reaction by the combination of ionic liquids as well as ultrasonication to produce superior results when compared to the simple conventional method. This methodology has the advantages of no usage of toxic catalysts and volatile organic solvents, yet a simple work-up procedure and high yields. Worthily, products can be separated from the ILs by ether and/or hexane solvent(s) washings. Convincingly, the catalyst could be recycled and reused for five cycles with no major loss in catalytic performance. Further, we confirm the stability of the recovered ionic liquids by the TGA and ¹HNMR techniques. This system affords a green and improved protocol over the reporting methods.
Effects of Ionic Liquids on the Nucleofugality of Chloride
2022, Journal of Organic Chemistry
The nucleofugality of chloride has been measured in solvent mixtures containing ionic liquids for the first time, allowing reactivity in these solvents to be put in context with molecular solvents. Using well-described electrofuges, solvolysis rate constants were determined in mixtures containing different proportions of ethanol and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the different solvent effects observed as the mixture changed could be explained using interactions of the ionic liquid with species along the reaction coordinate, determined using temperature dependent kinetic studies. The solvolysis data allowed determination of the nucleofugality of chloride in these mixtures, which varied with the proportion of salt in the reaction mixture, demonstrating quantitatively the importance of the amount of ionic liquid in the reaction mixture in determining reaction outcome. Nucleofugality data for chloride were determined in seven further ionic liquids, with the reactivity shown to vary over more than an order of magnitude. This outcome illustrates that the components of the ionic liquid are critical in determining reaction outcome. Overall, this work quantitatively extends the understanding of solvent effects in ionic liquids and demonstrates the potential for such information to be used to rationally select an ionic liquid to control reaction outcome.
Characterization of the acidity and basicity of green solvents by NMR techniques
2021, Magnetic Resonance Letters
The acidity and basicity of the solvents can influence the reaction outcome notably, and hence the precise measurement of pH is important for reaction. However, not all the pH values of organic solvents can be determined with a classic pH meter straightly. In this research, the acidity and basicity of environmentally friendly green solvents, such as ZnCl₂ molten salt hydrate, ionic liquids (ILs) and deep eutectic solvents (DESs), were characterized by ³¹P and ¹H NMR spectroscopy using trimethylphosphine oxide (TMPO) and pyrrole as probe molecules at 298 K. For the ZnCl₂ molten salt hydrate, the acidic strength of the ZnCl₂ molten salt hydrate increased with the concentration of ZnCl₂. By using the ¹H-pyrrole NMR approach, it was found that the base strength of amino acid-based ILs follows the order: [Ch][Lys] > [Ch][His].
Structure and properties of Ionic liquids: Green aspects
2021, Ionic Liquids in Analytical Chemistry: New Insights and Recent Developments
Ionic liquids comprise an important class of materials having vital applications in numerous research fields. In this chapter, an overview of the important properties of the ionic liquids and the effect of the different structural features on the properties of the ionic liquids has been presented. Also, various types of ionic liquids; their synthesis, properties, and applications are reviewed in the light of recent literature.

View all citing articles on Scopus

View full text

Diels-Alder reactions in room-temperature ionic liquids

Abstract

Tet. Lett.

Tet. Lett.

Tet. Lett.

Tetrahedron

Inorg. Chem.