Palladium-catalyzed cycloisomerization of (Z)-(2-en-4-ynyl)amines: a new synthesis of substituted pyrroles

(Z)-(2-En-4-ynyl)amines 1 bearing an internal triple bond undergo smooth cycloisomerization into pyrroles 2 in the presence of catalytic amounts of PdCl2 in conjunction with KCl at 25–100°C in anhydrous N,N-dimethylacetamide. When the triple bond is terminal, spontaneous uncatalyzed cyclization to the corresponding pyrroles takes place.