Reactions with 2‐mercaptopyrimidines. Synthesis of some new thiazolo[3,2‐a]‐ and triazolo[4,3‐a]pyrimidines

Alkylation of 5‐cyano‐4‐oxo‐6‐phenyl‐2‐thioxo‐1,2,3,4‐tetrahydropyrimidine I with methyl iodide, chloroacetic acid or 3‐chloro‐2,4‐pentanedione, afforded the S‐alkyl derivatives IIa‐c. 2‐Carboxymethylthio and 2‐(2′,4′‐dioxopentan‐3‐ylthio) derivatives IIb and IIc could be cyclised by acetic anhydride or polyphosphoric acid to give 6‐cyano‐3,5‐dioxo‐5H‐7‐phenylthiazolo[3,2‐a]pyrimidine III and 2‐acetyl‐6‐carboxamido‐5H‐3‐methyl‐7‐phenylthiazolo[3,2‐a]pyrimidine‐5‐one IX, respectively. Benzoylation of 2‐hydrazinopyrimidine derivative XII, in anhydrous dioxan, afforded the N‐benzoyl derivative XIII, which could be cyclised by heating in dimethylformamide to give 5‐amino‐6‐cyano‐3,7‐diphenyl‐s‐triazolo[4,3‐a]pyrimidine (XIV). The 2‐hydrazinopyrimidine derivatives XII and XV reacted with benzoyl isothiocyanate in dioxane to yield 4‐benzoylthiosemicarbazide derivatives XVI and XVII, which were converted into the 2‐s‐trizolopyrimidine derivatives XVIII and XIX, respectively. Also, XVI and XVII reacted with 2,4‐pentanedione and 3‐chloro‐2,4‐pentanedione to yield 2‐pyrazolopyrimidine derivatives XX and XXI, respectively.