Synergy or Competition between Palladium-Catalysis and KF/Alumina-Mediation for the Allylic Substitution of the Acetates of Baylis–Hillman Adducts by Phenols

The addition of various substituted phenols [XC6H4OH, X=H, o-CHO, o-CO2Me, o-CO2CH2Ph, o-CN, m-NHCOMe, m-OMe, p-OMe, p-CHO, p-Cl] to allylic acetates obtained from Baylis–Hillman adducts [RCH(OAc)C(CH2)CO2Et, R=H, n-Pr] has been studied in the presence of a Pd(0) catalyst and/or KF/alumina. In some cases, the use of one of these two reagents was sufficient to promote the OAc/OAr exchange but in general, faster reactions and higher yields were achieved when both reagents were used together. Evidence for two routes, an η3-allylpalladium intermediate and a Michael addition/elimination, was then obtained while a Heck type reaction could be involved under neutral conditions.