Efficient Regioselective Synthesis and Potential Antitumor Evaluation of Isoxazolo[5,4‐ b ]pyridines and Related Annulated Compounds

The reaction of 5‐amino‐3‐methylisoxazole with appropriate α,β‐unsaturated ketones gave the corresponding isoxazolo[5,4‐ b ]pyridines. Treatment of 1 with 2,6‐dibenzylidenecyclohexanone or 2‐benzylidenedimedone afforded the corresponding isoxazolo[5,4‐ b ]quinoline derivatives. 4,6,8,9‐Tetrahydroisoxazolo[5,4‐ b ]quinolin‐5‐one derivative was also obtained by multicomponent condensation reaction of 1 with dimedone and benzaldehyde. Heterocyclic annulation of the isoxazolo[5,4‐ b ]pyridine system was achieved via reaction of 1 with benzylidene derivatives of indandione, quinuclidone, pyrazolone, and oxazolone. A representative of some newly synthesized compounds was evaluated as antitumor agents.