Versatile 2‐aminothiazoles,building blocks for highly functionalised heterocycles

The reactions of quantitatively available 4‐phenyl‐ and 4‐(4‐antipyrinyl)‐2‐aminothiazole “4‐antipyrinyl‐” is used as a short‐term for “4‐(1,5‐dimethyl‐3‐oxo‐2‐phenyl‐2,3‐dihydro‐1‐H‐pyrazol‐4yl)‐”] with chloroacetyl chloride, acetic anhydride, ethyl cyanoacetate and carbon disulphide are reported. The products are transformed further by Knoevenagel condensations and coupling reactions with aromatic diazonium salts. The latter occur both at the thiazole ring and at the active methylene sites. The tautomerism of these products is studied on the basis of density functional theory calculations at the B3LYP/6‐31G* level.