Palladium-Catalyzed Construction of Polycyclic Heterocycles by an Alkyne Insertion and Direct Arylation Cascade

Cascade cyclization of bromoenynes bearing an aryl group withcatalytic amounts of palladium(II) acetate and cesium carbonateled to the direct construction of tri- or tetracyclic heterocycles.Direct arylation of a pyrrole, furan or thiophene ring in the cascadereaction affords the corresponding fused heteroarenes in moderateto good yields.