Synthesis of tetracyclic pyrrolidine/isoxazolidine fused pyrano[3,2-h]quinolines via intramolecular 1,3-dipolar cycloaddition in ionic liquid

Tetracyclic pyrrolidine/isoxazolidine fused pyrano[3,2-h]quinolines were synthesized via intramolecular 1,3-dipolar cycloaddition in ionic liquid. The transformations are operationally simple and environment-friendly in nature. The reaction is highly stereoselective affording exclusively the cis fused products, as deduced by the small coupling constant value (J = 4.8 Hz) between ring juncture protons which also showed clear NOESY correlation (in 5a and 5c). Confirmatory evidence came from single-crystal X-ray crystallography of 5d.