Mayr, H. and Ofial, A. R. and Sauer, Juergen and Schmied, B. (2000) [2(+)+4] cycloadditions of iminium tons - Concerted or stepwise mechanism of aza Diels-Alder reactions? EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (11). pp. 2013-2020. ISSN 1434-193X
Full text not available from this repository.Abstract
The N, N-dimethylmethyleneammonium ion 1 reacts regio-and stereoselectively with the 1,3-dienes 2a-2f to yield the 1,2,5,6-tetrahydropyridinium ions 3. The kinetics of these hetero Diels-Alder reactions, which have been followed by dilatometry and H-1-NMR spectroscopy obey second-order rate laws. Since the observed rate constants are only 30-300 times larger than those calculated for the stepwise process by the linear free-enthalpy relationship Ig k = s (E + N), it is concluded that these cycloadditions proceed in a stepwise manner or through pericyclic transition states that are not significantly stabilized by the concerted formation of two new a-bonds. In contrast, the reaction of the iminium ion 1 with cyclopentadiene (2g) yields 2,2-dimethyl-2-azoniabicyclo[2.2.1]hept-5-ene (3g) 2X10(4) times more rapidly than predicted for the stepwise cycloaddition process, indicating a free enthalpy of concert of 27 kJ mol(-1).
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | LINEAR FREE-ENERGY; ROTATIONAL BARRIER; BENZHYDRYL CATION; REACTIVITY; IONS; SELECTIVITY; KINETICS; ALKENES; SALTS; STEREOSELECTIVITY; carbocations; cycloadditions; kinetics; linear free-energy relationships; reaction mechanisms |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 26 Apr 2022 10:37 |
| Last Modified: | 26 Apr 2022 10:37 |
| URI: | https://pred.uni-regensburg.de/id/eprint/42424 |
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