Palladium-catalyzed 6-endo-dig oxycyclization-methoxycarbonylation toward the total synthesis of polymaxenolides

5-exo-Dig versus 6-endo-dig oxycyclizations of alkynols having an internal triple bond catalyzed by PdCl2, followed by methoxycarbonylation of the resulting vinylpalladium intermediates, are described. With an aim toward the total synthesis of polymaxenolides, a hybrid marine natural product containing a dihydropyran substructure, a model alkynol having the africane-type sesquiterpenoid skeleton was treated with PdCl2 and 1,4-benzoquinone in MeOH under an atmosphere of CO (balloon) to afford the desired 6-endo-dig oxycyclization-methoxycarbonylation product.