Synthesis of Densely Substituted α,β,γ,δ-Dienones via the Pd^II-Catalyzed Allylation, H-Migration, and Aerobic Oxidative δ-Hydride Elimination Cascade

A novel protocol for the highly stereoselective synthesis of E,E-α,β,γ,δ-unsaturated dicarbonyl compounds is presented. Starting from the readily available allylic alcohols and 1,3-diketones, an array of E,E-α,β,γ,δ-dienones can be efficiently synthesized in high yields via Pd-catalyzed dehydrative allylation, H-migration, and aerobic oxidative δ-hydride elimination cascade. In addition to the novel reaction mechanism, the use of 1:1 allylic alcohol and 1,3-diketone as reactant, 5 mol % of PdCl2 as catalyst, and 1 atm of environmentally benign O2 as oxidant, as well as the generation of only H2O byproduct, makes this protocol rapid, simple, atom-efficient, and clean.