Re-Catalyzed 3 + 3 Annulation for Rapid Assembly of Multisubstituted Pyridines from β-Enamino Esters and 1,3-Enynes/3-Ethynyl Indoles

Although rhenium-catalyzed annulation reactions are well-established, 3 + 3 annulations have remained elusive. We herein demonstrated a Re-catalyzed 3 + 3 annulation of β-enamino esters with 1,3-enynes affording a wide range of multisubstituted pyridines in good to excellent yields. Furthermore, 3-ethynyl indoles were also viable substrates undergoing indole ring-opening cyclization to furnish aniline-pyridine products. The protocol was readily scalable and featured simple catalyst and reaction conditions, thus offering a practical way for the construction of pyridine rings with controllable substitution patterns.