Regioselectivity in aromatic Claisen rearrangements.
Theoretical calculations and the isomeric product composition for a series of eight meta-substituted allyl aryl ethers confirm the reliability of a new (1)H NMR methodology used to predict aromatic Claisen regioselectivity from ground-state conformational preference of the reactant allyloxy group. Frontier HOMO-LUMO intramolecular orbital interactions, a classical approach in predicting reactivity and selectivity for Claisen rearrangements of allyl vinyl ethers, is shown to fail to mimic transition-state orbital interactions for aromatic Claisen rearrangements of meta-substituted allyl aryl ethers. B3LYP/6-31G(d,p) calculations on reactants and transition states are shown, however, to correctly predict the outcome of such aromatic Claisen rearrangements from either the preferential reactant ground-state conformation (theoretical predictions that agree with the NMR measurements) or the less energetic transition state, or both.
Gozzo
Fábio Cesar
FC
Institute of Chemistry, State University of Campinas-UNICAMP, CP 6154, 13083-970 Campinas, SP, Brazil.
Fernandes
Sergio Antonio
SA
Rodrigues
Denise Cristina
DC
Eberlin
Marcos Nogueira
MN
Marsaioli
Anita Jocelyne
AJ