## 2 Experimental
### General Procedure for the Preparation of 2-Aryldiendehydrazineyl-4-phenylthiazole **2a-d**
NMR \({}^{1}\)H (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 12.77 s (1H, OH), 11.68 s (1H, NH), 9.08 s (1H, OH), 8.43 s (1H, CH), 6.78 s (1H, Har), 2.66 s (2H, CH\({}_{2}\)), 2.32 s (2H, CH\({}_{2}\)), 1.37 s (9H, t-Bu), 1.33 (9H, t-Bu), 1.04 s (6H, 2 CH\({}_{3}\)). NMR\({}^{13}\)C (DMSO-d\({}_{6}\), \(\delta\), ppm): 189.3, 148.2, 142.6, 139.0, 136.8, 115.0, 113.1, 50.9, 35.6, 35.4, 35.0, 33.0, 29.6, 28.3. FT-IR, \(\
u\), cm\({}^{-1}\): 3458 (O-H), 1639 (C=O), 1598 (C=N Ar), 1573 (C=C Ar), 1369 (C=H Ar). Calc, %: C, 64.98; H, 7.50; N, 9.47; S, 7.23. Found, %: C, 64.90; H, 7.62; N, 9.45; S, 7.24. General Procedure for the Preparation of 2-((2,4-Arylidene)hydrazineylidene)thiazolidin-4-one **4a-d**  
Thiosemicarbazone **1a-d** (3 mmol), chloroacetic acid (3 mmol, 0.28 g), and sodium acetate (9 mmol, 0.74 g) were dissolved in acetic acid (20 mL). Reaction mixture was refluxed with stirring for 4-5 h, cooled to room temperature, poured into ice water, and the precipitate formed was filtered off and recrystallized from the appropriate solvent. 2-((2,4-dihydroxybenzylidene)hydrazineylidene)thiazolidin-4-one (**4a**) prepared from chloroacetic acid and **1a** (0.63 g). Yellow solid. Yield 45% (0.34 g), m.p. 339-340 \({}^{\circ}\)C (EtOH: H\({}_{2}\)O 2:1). NMR \({}^{1}\)H (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 11.02 s (1H, OH), 10.06 s (1H, OH), 8.47 s (1H, CH), 7.34 d (\(J\) = 9.0 Hz, 1H, Har), 6.37 d (\(J\) = 9.0 Hz, 1H, Har), 6.31 s (1H, Har), 3.93 s (2H, CH-C=O). NMR\({}^{13}\)C (DMSO-d\({}_{6}\), \(\delta\), ppm): 206.9, 174.2, 162.7, 161.9, 160.7, 158.8, 133.0, 110.9, 108.5, 102.9. FT-IR, \(\
u\), cm\({}^{-1}\): 3471 (O-H), 1678 (C=O), 1611 (C=N), 1597 (C=C Ar). Calc, %: C, 47.80; H, 3.61; N, 16.72; S, 12.76. Found, %: C, 47.75; H, 3.80; N, 16.65; S, 12.68. 2-((4-hydroxy-3-methoxybenzylidene)hydrazineylidene)thiazolidin-4-one (**4b**) prepared from chloroacetic acid and **1b** (0.68 g). Yellow solid. Yield 95% (0.76 g), m.p. 257-259 \({}^{\circ}\)C (EtOH: H\({}_{2}\)O 3:1). NMR \({}^{1}\)H (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 9.94 s (1H, OH), 8.23 s (1H, CH), 7.29 s (1H, Har), 7.15 d (\(J\) = 8.0 Hz, 1H, Har), 6.87 d (\(J\) = 8.0 Hz, 1H, Har), 3.83 s (2H, CH\({}_{2}\)), 3.77 s (3H, CH\({}_{3}\)). FT-IR, \(\
u\), cm\({}^{-1}\): 3554 (O-H), 1684 (C=O), 1637 (C=N), 1585 (C=C Ar). Calc, %: C, 49.80; H, 4.18; N, 15.84; S, 12.09. Found, %: C, 49.76; H, 4.29; N, 15.82; S, 12.12. 2-((3,5-di-_tert_-butyl-4-hydroxybenzylidene)hydrazineylidene)thiazolidin-4-one (**4c**) prepared from chloroacetic acid and **1c** (0.93 g). Yellow solid. Yield 89% (0.79 g), m.p. 308-310 \({}^{\circ}\)C (EtOH: H\({}_{2}\)O 3:1). NMR \({}^{1}\)H (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 11.91 s (1H, NH), 8.27 s (1H, CH), 7.53 s (2H, Har), 7.48 s (1H, OH), 3.82 s (2H, CH\({}_{2}\)), 1.37 s (18H, t-Bu). \({}^{13}\)C NMR (DMSO-d\({}_{6}\), \(\delta\), ppm): 177.7, 156.5, 144.6, 139.6, 127.4, 125.7, 124.5, 55.4, 35.0, 30.7. FT-IR, \(\
u\), cm\({}^{-1}\)2-((4,6-di-_tert_-butyl-2,3-dihydroxybenzylidene)hydrazineylidene)thiazol-4-one (**4d**) prepared from chloroacetic acid and **1d** (0.97 g). Yield 88% (0.96 g), m.p. 258-260 \({}^{\circ}\)C \({}^{1}\)H NMR (DMSO-d6, \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 12.26 (s, 1H, OH), 12.03 (s, 1H, NH), 9.18 (s, 1H, OH), 8.45 (s, 1H, CH), 6.81 (s, 1H, Har), 4.02 (s, 2H, CH\({}_{2}\)), 1.39 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu). 13C NMR (DMSO-d6, \(\delta\), ppm): 174.4, 172.4, 164.5, 149.3, 142.6, 139.6, 137.4, 112.8, 35.5, 35.4, 34.2. FT-IR, v, cm\({}^{-1}\): 3499 (O-H), 1677 (C=O), 1623 (C=N), 1599 (C=C Ar). Calc, %: C, 59.48; H, 6.93; N, 11.56; S, 8.82. Found, %: C, 59.31; H, 7.01; N, 11.59; S, 8.78. General Procedure for the Preparation of 2-(2-Arylidene)hydrazineylidene)-4-oxothiazolition-5-ylylacetic Acid **5a-d**  
Thiosemicarbazone **1a-d** (1.63 mmol) and maleic anhydride (1.79 mmol, 0.18 g) were dissolved in acetic acid (15 mL).