Intermolecular Dehydrogenative Heck Reactions

Intermolecular dehydrogenative Heck reaction (DHR), leading to the formation of a C-C bond from two C-H bonds, is discussed. For the stoichiometric DHRs carried out in AcOH or in solvent mixtures containing AcOH, it is found that AcOH could act as an ionizing agent protoning off an acetate ligand to afford [ArPd(II)]+ species. Studies on the Mizoroki-Heck reaction of allylic acetates have shown that the presence of Ag(I) avoids the β-elimination of the OAc and OCO2Me groups. A study of Pd(OAc)2-catalyzed alkenylation of o-heterosubstituted arylbenzenes shows the formation of complex via a Heck-type reaction. The synthesis of coumarins from the DHR of phenols with ethyl acrylates, at room temperature in CF3CO2H, shows the mildness of the reaction conditions due to in situ formation of a catalyst with an increased reactivity.