Palladium(II)-catalyzed coupling of allenoic acids and α,β-unsaturated carbonyl compounds through tandem intramolecular oxypalladation and conjugate addition reactions

A regioselective divalent palladium-catalyzed tandem coupling reaction of allenoic acids with α,β-unsaturated carbonyl compounds was developed. The reaction involves intramolecular oxypalladation of an allene, followed by insertion of the α,β-unsaturated carbonyl compound and protonolysis of the CPd bond to regenerate the Pd(II) species in the presence of excess halide ions. Functionalized lactones, tetrahydropyranones and dihydropyranones can be synthesized with high regioselectivity in one step.