Sulfamic Acid-functionalized Nano-titanium dioxide as a Novel and Highly Efficient Heterogeneous Nanocatalyst for One-pot and Solvent-free Synthesis of Hexahydroquinolines

Hexahydroquinolines are synthesized via one-pot, four-component condensation of 1,3-cyclic diketones, aromatic aldehydes, malononitrile, and ammonium acetate in the presence of sulfamic acid-functionalized nano-titanium dioxide as a novel type of heterogeneous nanocatalyst. The optimized reaction condition is achieved using response surface method (Box–Behnken design [BBD]). Operational simplicity, low cost, nontoxic nature, and high reusability of the catalyst together with simple work-up and excellent product yields are the main advantages of this methodology. Also, the nanocatalyst can be recovered easily by centrifugation and reused efficiently for at least seven consecutive runs.