## 2 Experimental
### General Procedure for the Preparation of Thiosemicarbazones **1a-d**  
The solution of thiosemicarbazide (11 mmol) in 40 mL mixture of ethanol and acetic acid (1:1) was stirred under reflux for 3-4 h. Reaction mixture was cooled to room temperature and poured into ice water, and the precipitate formed was filtered off and recrystallized from isopropanol.  
2,4-dihydroxybenzaldehyde thiosemicarbazone (**1a**) was prepared from thiosemicarbazide and 2,4-dihydroxybenzaldehyde (1.52 g).  
White powder. Yield 87% (2.02 g), m.p. 235-236 \({}^{\circ}\)C (lit. 237-238 \({}^{\circ}\)C [37]). \({}^{1}\)H NMR (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 9.98 s (1H, OH), 9.65 (br.s. 1H, NH), 7.99 s (1H, CH), 7.50 d (\(J\) = 9.0 Hz, 1H, Har), 6.26 s (1H, Har), 6.22 d (\(J\) = 9.0 Hz, 1H, Har). FT-IR, \(\upsilon\), cm\({}^{-1}\): 3673 (O-H), 1618 (C=N), 1500, 1232, 1110 (C-O). Calc., %: C 45.49; H 4.29; N 19.89; S, 15.18. Found, %: C 45.62, H 4.43, N 19.87, S 15.15.  
4-hydroxy-3-methoxybenzaldehyde thiosemicarbazone (**1b**) was prepared from thiosemicarbazide and vanillin (1.67 g).  
White powder. Yield 91% (2.25 g), m.p. 196-198 \({}^{\circ}\)C (lit. 197 \({}^{\circ}\)C [38]). \({}^{1}\)H NMR (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): \(\delta\) 11.20 s (1H, NH), 9.51 s (1H, OH), 8.04 s (1H, CH), 7.90 s (2H, NH\({}_{2}\)), 7.43 s (1H, Har), 7.03 d (\(J\) = 9.0 Hz, 1H, Har), 6.74 d (\(J\) = 9.0 Hz, 1H, Har), 4.01 s (3H, O-CH\({}_{3}\)). NMR\({}^{13}\)C (DMSO-d\({}_{6}\), \(\delta\), ppm): 177.8 (NH\({}_{2}\)C=S), 149.2 (Car-OH), 148.5 (Car-O-CH\({}_{3}\)), 143.5 (CH=N), 126.0, 122.8, 115.7, 109.7, 56.2 (O-CH\({}_{3}\)). FT-IR, \(\upsilon\), cm\({}^{-1}\): 3528 (O-H), 3436 (N-H), 3274 (N-H), 1586 (C=N Ar), 1544 (C=C Ar), 1276 (C-N), 850, 836, 816 (C-H Ar). Calc., %: C 47.99; H 4.92; N 18.65; S, 14.23. Found, %: C 47.82, H 5.03, N 18.61, S 14.30.  
3,5-di-_tert_-butyl-4-hydroxybenzaldehyde thiosemicarbazone (**1c**) was prepared from thiosemicarbazide and 3,5-di-_tert_-butyl-4-hydroxybenzaldehyde (2.57 g).  
White powder. Yield 89% (3.01 g), m.p. 183-184 \({}^{\circ}\)C. \({}^{1}\)H NMR (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 11.19 s (1H, NH), 7.94 s (1H, CH), 7.41 s (2H, Har), 7.33 s (1H, OH), 1.37 s (18H, t-Bu).  
\({}^{13}\)C NMR (DMSO-d\({}_{6}\), \(\delta\), ppm): 8 177.7 (NH\({}_{2}\)C=S), 156.5, 144.6, 139.6, 139.1, 127.35, 125.7, 124.5, 35.0 ((CH\({}_{3}\))\({}_{3}\)C), 30.7 ((CH\({}_{3}\))\({}_{3}\)C). FT-IR, \(\upsilon\), cm\({}^{-1}\): 3624 (O-H), 3453 (N-H), 3236 (N-H), 3155 (N-H),1604 (C=N Ar), 1533 (C=C Ar), 1294 (C-N), 889, 837 (C-H Ar). Calc., %: C 6.251; H, 8.20; N, 13.67; S, 10.43. Found, %: C 62.37, H 8.31, N 13.62, S 10.45.  
4,6-di-_tert_-butyl-2,3-dihydroxybenzaldehyderhoea thiosemicarbazide (**1d**) was prepared from thiosemicarbazide and 3,5-di-_tert_-butyl-4-hydroxybenzaldehyde (2.75 g).  
White powder. Yield 82% (2.91 g), m.p. 191-193 \({}^{\circ}\)C. \({}^{1}\)H NMR (DMSO-d\({}_{6}\), \(\delta\), ppm, \({}^{3}\)\({}_{\rm HH}\), Hz): 11.58 s (1H, NH), 10.27 s (1H, OH), 8.91 s (1H, CH), 8.18 s (2H, NH\({}_{2}\)), 7.91 s (1H, OH), 6.76 s (1H, Har), 1.34 s (9H, t-Bu). 13C NMR (DMSO-d\({}_{6}\), \(\delta\), ppm): 197.9 (NH\({}_{2}\)C=S), 172.5, 153.1, 146.7, 142.7, 139.3, 136.2, 35.6 ((CH\({}_{3}\))\({}_{3}\)C), 35.3((CH\({}_{3}\))\({}_{3}\)C), 32.8 ((CH\({}_{3}\))\({}_{5}\)C). FT-IR, \(\upsilon\), cm\({}^{-1}\): 3467 (N-H), 1610 (C=N), 1587 (C=C), 1293, 1080 (C-O). Calc., %: C 59.41; H 7.79; N 9.89; S 9.91. Found, %: C 59.30; H 7.75; N 9.83; S 9.88.