DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels-Alder reactions between several α-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated α-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism.

Legnani, L., Lunghi, C., Marinone, F., Nativi, C., Richichi, B., Toma, L. (2007). Alternative mechanistic paths in the hetero-Diels-Alder reaction of alpha-oxothiones: a theoretical study. EUROPEAN JOURNAL OF ORGANIC CHEMISTRY(21), 3547-3554 [10.1002/ejoc.200700112].

Alternative mechanistic paths in the hetero-Diels-Alder reaction of alpha-oxothiones: a theoretical study

LEGNANI, LAURA;
2007

Abstract

DFT calculations at the B3LYP/6-311+G(d,p) level for the C, H, and O atoms and at the 6-311+G(2df,p) level for the S atom were used to study the hetero-Diels-Alder reactions between several α-oxothiones and ethylene or methyl vinyl ether (MVE). All the transition states and the intermediates along the reaction pathways, as well as the reaction products, were located. The reactions with ethylene are all concerted though asynchronous whereas in the reactions with MVE the electron-releasing character of the methoxy substituent lowers the energy barriers and enhances the asynchronicity and the charge transfer process to such an extent that the reaction may become unconcerted and exhibit a two-step mechanism with a zwitterionic intermediate derived from nucleophilic attack of electron-rich MVE to the sulfur atom of the strongly electrophilically activated α-oxothiones. The reactions are also favored by the conjugation of the newly formed C=C bond. Moreover, the geometric features of the diene exert a nonnegligible role, as dienes that are planar or almost planar in their ground state show a lower energy barrier. Thus, both geometric and electronic features of the dienes as well as of the dienophiles play a significant role in the easiness of the reactions and in their mechanism.
Articolo in rivista - Articolo scientifico
Charge transfer; Cycloaddition; Density functional calculations; Transition states;
English
3547
3554
8
Legnani, L., Lunghi, C., Marinone, F., Nativi, C., Richichi, B., Toma, L. (2007). Alternative mechanistic paths in the hetero-Diels-Alder reaction of alpha-oxothiones: a theoretical study. EUROPEAN JOURNAL OF ORGANIC CHEMISTRY(21), 3547-3554 [10.1002/ejoc.200700112].
Legnani, L; Lunghi, C; Marinone, F; Nativi, C; Richichi, B; Toma, L
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/351976
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