The mixture of 4-amino functionalized azo benzene (1 mmol) (1), pertinent aryl aldehyde derivatives (1 mmol) 2(a–r), indoline-2,3-dione (1 mmol) (3), ammonium acetate (1 mmol) (4) and a catalytic amount of l-proline (5 mol%) were sonicated in the presence of ethanol (10 ml).
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