Synthesis of Isoxazolopyridines and Spirooxindoles under Ultrasonic Irradiation and Evaluation of Their Antioxidant Activity

New polycyclic-fused isoxazolo[4,5-e] pyridines and spirooxindoles were obtained via multicomponent reaction of 5-amino-3-methylisoxazole, indan-1,3-dione, and aromatic aldehydes and reaction of 5-amino-3-methylisoxazole, isatin, and beta-diketones in the presence of (+/-)-camphor-10-sulfonic acid as an effective and nontoxic organocatalyst under ultrasound-promoted conditions. The antioxidant activity of the novel synthesized compounds was studied.