ZnFe2O4 nano-catalyzed facile synthesis of tetrahydropyranoquinoline derivatives (4a–f) via one-pot multi-component Povarov’s inverse-electron-demand hetero Diels–Alder reaction of substituted aromatic aldehyde (1), aromatic amine (2) with dihydrofuran (3) under ultrasonic irradiation. This may be h...