Bromination of 6-methyl-2-thiouracil (I) gave the 5-bromo analogue II. Alkylation of each of I and II yielded the S-alkyl derivatives IIIa-g. Cyclisation of IIIa,c gave the 3,7-dimethylthiazolo[3,2-a]pyrimidines VIIa,b. The 2-arylmethylenethiazolo[3,2-a]pyrimidines VIa-i were synthesized via the reaction of either I or II with a mixture of chloroacetic acid and aromatic aldehydes. The 2-methylthiopyrimidine analogue VIII reacted with aromatic amines to produce the 2-arylamino derivatives IXa,b. Condensation of the 2-hydrazino analogue X with aromatic aldehydes formed the Schiff's bases XIa-e. The analogue XIb could be cyclised by bromine into the 6-bromo-s-triazolo[4,3-a]pyrimidine derivative XIII. The reaction of X with each of carbon disulphide and chloroacetyl chloride gave the s-triazolo[4,3-a]pyrimidine XVII and pyrimido[2,1-c]-as-triazine XIX derivatives, respectively. Also, compound X reacted with either 2,4-pentanedione, 3-chloro-2,4-pentanedione or 1,1,1-trifluoro-2,4-pentanedione to form the 2-pyrazolylpyrimidines XXIa-c, respectively. Malononitrile added to XXII to yield the dipyrimidino-[2,1-b: 1',2'-c]thiazine XXIII with a new ring system.
