Fe₃O₄@SiO₂-NH-GA-[(CH₂)₄-SO₃H]₃ catalyzed the synthesis of acridine-1,8-diones^a.

Entry 1: 4a, 90%b	Entry 2: 4b, 88%	Entry 3: 4c, 94%
Entry 4: 4d, 96%	Entry 5: 4e, 85%	Entry 6: 4f, 87%
Entry 7: 4g, 87%	Entry 8: 4h, 81%	Entry 9: 4i, 80%
Entry 10: 4j, 80%	Entry 11: 4k, 74%c	Entry 12: 4l, 70%c
Entry 13: 4m, 83%	Entry 14: 4n, 84%	Entry 15: 4o, 84%
Entry 16: 4p, 87%	Entry 17: 4q, 73%	Entry 18: 4r, 77%
Entry 19: 4s, 78%	Entry 20: 4t, 94%	Entry 21: 4u, 96%
Entry 22: 4v, 92%	Entry 23: 4w, 94%

^aExperimental conditions: aldehyde (1.0 mmol), dimedone (2.0 mmol), and ammonium acetate/amines (1.1 mmol), catalyst (5.0 mg), in water (2.0 mL) at 60 °C.

^bIsolated yield.

^cThe reaction was performed in a sealed tube.