Synthesis of unsaturated lactones via palladium-catalyzed cyclization of alkenoic acids

Acyclic and cyclic, aliphatic or aromatic, 4- or 5-alkenoic acids cyclize in high yield to 5- or 6-membered unsaturated lactones using 5 mol % Pd(OAc) 2 , 2 equiv of NaOAc, and 1 atm of O 2