## 2 Results and Discussion  
### Synthesis  
The focus of this research paper, 4-antipyrinyl-2-chloroacetamidothiazole (**1**), has been obtained by stirring 2-amino-4-antipyrinylthiazole with chloroacetyl chloride in DMF and triethylamine for 4 h [30]. Heating of chloroacetamide derivative **1** with ethyl thioglycolate in absolute ethyl alcohol and sodium acetate furnished one product (TLC), which was identified as ethyl 2-[(2-((4-antipyrinylthiazol-2-yl)amino)-2-oxoethyl)[thio]acetate (**2**) based on its spectral and elemental analyses, see Scheme 1. Chloroacetamide derivative **1** reacted with 3-cyano-4,6-dimethyl-2-mercaptoethanolpyridine (**3**) in acetone and sodium carbonate to afford _N_-(4-antipyrinylthiazol-2-yl)-2-((3-cyano-4,6-dimethylpyridin-2-yl)thio)-acetamide (**4**), which underwent intramolecular cyclization in hot ethanolic sodium ethoxide solution furnishing the conforming 3-aminothieno[2,3-\(b\)]pyridine derivative **5**, as shown in Scheme 1. The formation of **5** may be interpreted through the nucleophilic attack of active methylene on the cyano group according to the mechanistic consideration. Structural proof of **4** and **5** was verified from their compatible spectral analyses including IR, \({}^{1}\)H NMR, and \({}^{13}\)C NMR. The infrared spectrum of **4** revealed the absorption of nitrile function at 2219 cm\({}^{-1}\) that disappeared from the infrared spectrum of compound **5**, indicating the cyclization process had occurred. The \({}^{1}\)H NMR spectrum of **4** displayed the two protons of the methylene group as a singlet signal at 4.05 ppm, this signal was no longer present in the spectrum of the product **5**, providing additional evidence for the successful cyclization reaction. The reactivity of C-5 of thiazole ring in the key compound, 4-antipyrinyl-2-chloroacetamidothiazole (**1**) towards electrophilic diazo-coupling reaction was investigated. Thus, the coupling reaction of compound **1** with diazotized sulphanilamide was carried out in ethanol containing sodium acetate at 0-5 \({}^{\circ}\)C to furnish 4-antipyrinyl-2-chloroacetamido-5-(4-sulfamoyliphenylazo)thiazole (**6**), see Scheme 2. The infrared spectrum of **6** showed three characteristic absorptions at 3351, 3264, and 1697 cm\({}^{-1}\) to indicate the presence of -NH\({}_{2}\), N-H, and C=O functional groups, respectively. The \({}^{1}\)H NMR spectrum displayed four singlet signals at \(\delta\) 2.72 ppm for three protons of CH\({}_{3}\)-C, at \(\delta\) 3.28 ppm for three protons of CH\({}_{3}\)-N, at \(\delta\) 4.44 ppm for two protons of -CH\({}_{2}\)- group, and at \(\delta\) 12.92 ppm for one proton of N-H. In addition, a multiplet signalfor the aromatic protons and NH\({}_{2}\) (\(\$\) 7.28-7.61 ppm), and a doublet signal for the two protons at \(\$\) 7.94-8.00 ppm (AA'-BB' system of the 1,4-disubstituted phenyl ring). The reaction of 2-chloroacetamido-thiazole derivative **6** with 2-mercaptoethanolbenzothiazole and/or 2-mercaptoethanolbenzoxazole was achieved by refluxing in ethyl alcohol and sodium acetate for 2 h to furnish the corresponding sulfide derivatives **7a** and **7b**, respectively. The chemical structures of **7a** and **7b** were deduced from their compatible spectral and elemental analyses. Treatment of the key compound **1** with ammonium thiocyanate in refluxing ethanol has been described to furnish 2-((4-antipyrinylthiazol-2-yl)imino)thiazol-4-one (**9**). A plausible mechanism for the reaction is indicated in scheme 3. The reaction proceeds via intramolecular cyclization of the thiocyanate intermediate **8** and the Dimroth-like rearrangements [31]. The product of this reaction was designed as the lactam derivative **9** and finds support from the literature of [PERSON] et al. [32].