Intra- and intermolecular hetero-Diels-Alder reactions. 16. Stereospecificity in intramolecular hetero-Diels-Alder reactions of 2-benzylidene-1,3-dicarbonyl compounds
Intra- and intermolecular hetero-Diels-Alder reactions. 17. Intramolecular hetero-Diels-Alder reaction of alkylidene- and benzylidenepyrazolones and benzylideneisoxazolones. Investigations toward the conformation of the transition state
作者:Lutz F. Tietze、Thomas Brumby、Martina Pretor、Gerd Remberg
DOI:10.1021/jo00239a024
日期:1988.2
Intramolecular Diels−Alder Reaction in Ionic Liquids: Effect of Ion-Specific Solvent Friction
作者:Shraeddha Tiwari、Nageshwar Khupse、Anil Kumar
DOI:10.1021/jo801802q
日期:2008.11.21
The present work aims at understanding the role of viscosity or solvent friction in ionic liquids for an intramolecular Diels-Alder (IMDA) reaction of (E)-1-phenyl-4-[2-(3-methyl-2-butenyloxy)benzylidene]-5-pyrazolone (1). The results have been analyzed on the basis of the current theoretical models, and their failure to account for the observed trends is discussed in terms of "effective" viscosity or microviscosity. The rates of the reaction decrease with the increasing viscosity of the ionic liquids. As evident from the anionic effect, the solute-solvent specific interactions play a role in governing the kinetics of the reaction. The lower viscosities of the bistrifluoromethanesulfonimide [NTf2](-) based ionic liquids as compared to those based on tetrafluoroborate [BF4](-) anion fail to result in a corresponding acceleration in the rates of the reaction. These contradictory results indicate that solvent microviscosity, rather than the bulk macroscopic viscosity, should be the criteria for selecting the ionic liquids as reaction media.
Intra- and intermolecular hetero-Diels-Alder reactions. 16. Stereospecificity in intramolecular hetero-Diels-Alder reactions of 2-benzylidene-1,3-dicarbonyl compounds
作者:Lutz F. Tietze、Matthias Bratz、Reinhard Machinek、Guenter V. Kiedrowski