A Tandem Cyclization–Allylation Approach to Allylated Pyranoquinoline Derivatives

Introduction: Pyranoquinoline derivatives constitute an important class of fused N-heterocycles that exhibit diverse biological activities, including anticancer, antimicrobial, and anti-inflammatory properties. Owing to their significant pharmacological potential, the development of efficient synthetic methodologies for the construction and functionalization of pyranoquinoline frameworks remains an active area of research. In particular, allylated heterocycles are valuable synthetic intermediates, as the allyl group serves as a versatile handle for further structural diversification. Herein, we report a sequential AgNO₃-catalyzed cyclization and BF₃·Et₂O-mediated allylation strategy for the efficient synthesis of allylated pyranoquinoline derivatives.

Methods: The synthetic strategy involved AgNO₃-catalyzed cyclization of ortho-alkynyl quinoline aldehydes in the presence of alcohols to generate pyranoquinoline intermediates. Subsequent treatment with allyltributyltin under BF₃·Et₂O promotion afforded the corresponding allylated products. The scope of the methodology was evaluated using various substrates, and all synthesized compounds were characterized by NMR spectroscopy and HRMS.

Results: The sequential cyclization–allylation protocol efficiently furnished allylated pyranoquinoline derivatives in good to excellent yields. The methodology exhibited broad substrate scope and tolerated a variety of substituents, providing rapid access to structurally diverse allylated fused heterocyclic scaffolds under mild conditions.

Conclusion: A sequential cyclization–allylation strategy has been developed for the efficient synthesis of allylated pyranoquinoline derivatives. The protocol features mild reaction conditions, broad substrate scope, and good to excellent yields, offering a practical approach for the rapid construction and functionalization of biologically relevant fused heterocyclic scaffolds.