Condensation of a ternary mixture of ethyl cyanoacetate, S‐methylisothiourea and aromatic aldehydes in pyridine afforded directly the 4‐aryl‐5‐cyano‐2‐methylthio‐6‐oxopyrimidines IV in good yields. Alkylation of IV with alkyl halides in alkaline medium yielded the 1‐alkyl derivatives V. The methylthio group in IV and V could be eliminated by aniline, hydrazine and phenylhydrazine and the corresponding 2‐anilino, VII, 2‐hydr‐azino, VIIIa,b, and 2‐phenylhydrazino, VIIIc,d, derivatives were obtained. Compounds VIIIa,b could be cyclised with nitrous acid to give the 3‐cyano‐4‐phenyltetrazolo[1,5‐a]pyrimidine‐2‐one (Xa) and the 1‐methyl analogue Xb, respectively. Some derivatives of VIII were prepared to help in elucidating the structures.

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3‐Arylacrylonitrile‐2‐thiocarboxamides (1a–d) reacted with S‐methylisothiourea to give 4‐amino‐6‐aryl‐2‐methylmercaptopyrimidine‐5‐carbonitriles (3a–d). The products 3a–d were also obtained via the reaction of 3‐arylacrylonitrile‐2‐carbonitriles (4a–d) with S‐methylisothiourea. Compounds 4a–d reacted with thiourea and urea to yield 4‐amino‐6‐aryl‐2‐mercaptopyrimidine‐5‐carbonitriles (5a–d) and 2‐hydroxy derivatives (5e–h) respectively. Oxidation of 5a–d with hydrogen peroxide afforded 5e–h. 5a–h were readily alkylated with methyl iodide to give 3a–d.

2‐Carboxy‐1‐alkylindole‐3‐acetic acid anhydrides (I) condensed with S‐methylisothiosemicarbazide in DMF to form 5,11‐dihydro‐6‐methyl‐2‐methylthioindolo[3′,2′:4,5]pyrido[1,2‐b]‐s‐triazol‐5‐one (II). Compound II underwent ring opening on refluxing with sodium hydroxide solution to give IV. The anhydride I reacted with primary amines in benzene to give 2‐carboxy‐1‐alkylindole‐3‐acetanilide derivatives (VI) which yielded l‐methylindole‐3‐acetic acid by decarboxylation followed by hydrolysis. Compound II oxidised to the diketo compound X which could be prepared by the hydrolysis of the azomethine derivative IX with acetic acid‐hydrochloric acid mixture. Compound II reacted with benzyl chloride to yield the dibenzyl derivative XII, condensed with p‐chlorobenzaldehyde to form the 11‐p‐chlorobenzylidene derivative XI and coupled with arenediazonium salt to give the 11‐arylhydrazone derivatives XIII.