Mechanisms and Conformational Control of (4 + 2) and (2 + 2) Cycloadditions of Dienes to Keteniminium Cations.
J Org Chem
; 85(4): 2597-2606, 2020 02 21.
Article
en En
| MEDLINE
| ID: mdl-31917921
ABSTRACT
Selectivities in (4 + 2) and (2 + 2) cycloadditions of keteniminium cations with 1,3-dienes studied experimentally by Ghosez et al. were explored with ωB97X-D density functional theory. Reactions of keteniminium cations with 1,3-dienes are influenced by the s-cis or s-trans nature of the diene. s-Trans dienes react to give an intermediate enamine that leads to favored formation of (2 + 2) cycloadducts across the keteniminium C-C bond. The first step of the cycloaddition is rate-determining, and reaction occurs by attack on the central carbon of the keteniminium cation and subsequent C-C bond formation. In contrast, s-cis constrained dienes lead to preferential formation of (4 + 2) products by both stepwise and concerted mechanisms involving regioselective addition to the keteniminium C-N bond. Diels-Alder reaction occurs via a concerted mechanism if the diene termini are held in close proximity, as in cyclopentadiene.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Polienos
Idioma:
En
Revista:
J Org Chem
Año:
2020
Tipo del documento:
Article
País de afiliación:
Estados Unidos