General scheme for the synthesis of compounds 4–10, 13–19 and 22–28. Reagents and conditions: (i) Acetic anhydride, reflux, 2–3 h, (ii) Propionic anhydride, reflux, 2–3 h, (iii) benzoyl chloride, pyridine, stirring, 1 h, (iv) Ethyl-2-amino-4-thiazoleacetate, pyridine, reflux, 5–6 h, (v) substituted amines, pyridine, sodium acetate, stirring, 0–5 oC, 7–10 h.