Methyl substituent effects in radical cation Diels-Alder reactions.
J Org Chem
; 72(2): 559-66, 2007 Jan 19.
Article
en En
| MEDLINE
| ID: mdl-17221974
The effect of methyl substitution on the Diels-Alder radical cation reaction was studied using B3LYP with a 6-31G* basis set. Five separate pathways, one concerted and four stepwise, were examined for each possible position of a methyl substituent. None of the concerted transition structures could be located without symmetry constraints, and all but one of the structures obtained under these conditions were destabilized by a second-order Jahn-Teller distortion. A concerted pathway with simultaneous bond formation at C1 and C4 is therefore excluded. Stepwise pathways that had the methyl group either on a carbon involved in the initial bond formation or in a position where it could not stabilize the radical/cation were a few kcal/mol above alternate pathways. High transition state energies for the formation of vinylcyclobutane derivatives cause it to be a minor product in general. The pathway that proceeds through an anti-intermediate is the most favored, while the pathways forming the gauche-out intermediate that converts to the anti-intermediate is also strongly represented. Both of the major pathways lead directly to the formation of the methylcyclohexene product.
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01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
J Org Chem
Año:
2007
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Estados Unidos