Alkylation of 6-aryl-4-oxo-2-thioxopyrimidine-5-carbonitriles (1a-c) afforded the key intermediates 2a-e, which underwent further alkylation at N-3 nitrogen atom, upon treatment with α-halofunctionalized compounds, namely: ethyl bromoacetate, chloroacetone, chloroacetylacetone, chloroacetonirile, or monobromomalononitrile to perform 2-alkylthio-6-aryl-5-cyano-4-oxo-3-substituted-3,4-dihydropyrimidines 7-9. Heating 7-9 with hydrazine hydrate produced imidazo[1,2-a]pyrimidine derivatives 10-15. Treatment of 10a with each of ethyl cyanoacetate, ethyl acetoacetate, or acetylacetone gave pyrazoloimidazopyrimidine derivatives 18a,b, 19, respectively. Compound 10a reacted with carbon disulphide to give oxazoloimidazopyrimidine20. Reaction of the imidazopyrimidine derivative 15a with glacial acetic acid or thiourea afforded triazoloimidazopyrimidines21,22. Also, compound 15aunderwent cycloaddition reaction upon treatment with either of phthalic anhydride or acrylonitrile to give 2-phenyl-4,12- dioxopyrimidino[2``,1``:2`,3`]imidazo[1`,5`:2,3][1,2,4]triazolo[1,5-b]isoindole-3-carbonitrile (23) or 8-amino-2- phenyl-4-oxo-7H-pyrimido[2`,1`:2,3]imidazo[1,5-b][1,2,4]triazepine-3-carbonitrile (24), respectively. Imidazo pyrimidines 15d,e underwent cyclocondensation upon heating with each of formic acid, formamide/ formic acid or ammonium thiocyanate to produce the pyrimido[2,1-f]purine derivatives 25a,b, 26,and 27,respectively.
