Tetrabutylammonium bromide and K2CO3: an eco-benign catalyst for the synthesis of 5-arylidene-1,3-thiazolidine- 2,4-diones via Knoevenagel condensation

摘要

Phase-transfer catalyzed, energy-efficient and facile synthesis of 5-arylidene-1,3-thiazolidine-2,4-diones was developed. Three independent variables (temperature, bases and phase-transfer catalyst (PTC)) were screened through one-factor-at-a time (OFAT) study. The optimum reaction conditions suggested by the OFAT analysis were the use of tetrabutylammonium bromide (8 mol) and potassium carbonate (1 mmol) for the reaction at 100 degrees C. The nitrogen of PTC stabilizes carbonyl groups of thiazolidine-2,4-dione (TZD). The active methylene hydrogen of TZD forms potassium salt with potassium carbonate and generates 5-arylidene-1,3-thiazolidine-2,4-diones (1-16) through nucleophilic attack on the carbonyl carbon of arylaldehydes. The prominent advantages of this new process are economic viability, shorter reaction time (15 min), simple product isolation (non-chromatographic method), good to excellent yields (78-96) and solvent-free conditions.