Fe3O4@SiO2 functionalized sulfonic acid (FSSA) was prepared by a facile method in three steps and characterized by XRD, FT-IR, SEM-EDX, TGA, UV-Vis, and VSM techniques. The XRD pattern shows the characteristic peaks of the cubic structure of Fe3O4. The presence of sulfonic acid groups was confirmed by FT-IR analysis. FSSA shows reasonable magnetic parameters with good saturation magnetization (Ms = 22.61 memu/g). FSSA was used as a catalyst for the preparation of chromeno[4,3-d]pyrido[1,2-a]pyrimidin derivatives via the condensation of 4-hydroxycoumarin, aldehydes, and 2-aminopyridines under reflux in EtOH (50%) as well as US irradiation. The effect of solvent, temperature, and catalyst dosages on the product formation under reaction conditions was investigated. The effect of various Lewis and Bronsted acid catalysts was compared with FSSA and among different catalysts screened, FSSA was found to have the best efficiency. Next, FSSA was used for the effective and high yielding preparation of 14-aryl-14H-dibenzo[a,j]xanthene derivatives, N-((2-hydroxynaphthalen-1-yl)(aryl)methyl)acetamide derivatives, 2,4,5-triaryl-1H-imidazole derivatives, and 2-amino-5-oxo-4-aryl-4H,5H-pyrano[3,2-c]chromene-3-carbonitrile derivatives. Simple procedure, good yields, and short reaction times, as well as catalyst recovery, are the key advantages of this work.