Studies on 2-Arylhydrazononitriles: Synthesis of 3-Aryl-2-arylhydrazopropanenitriles and Their Utility as Precursors to 2-Substituted Indoles, 2-Substituted-1,2,3-Triazoles, and 1-Substituted Pyrazolo[4,3-d]pyrimidines

Coupling of 2-benzylmalononitrile with aromatic diazonium salts afforded 3-phenyl-2-arylhydrazonopropanenitriles 4a, b, which were rearranged into 2-cyanoindoles 5a, b upon heating with ZnCl2 in the presence of glacial acetic acid. The produced indole derivatives 5a, b can be successfully used as valuable precursors to synthesize 1,2,4-oxadiazolylindoles 8a, b. The reaction of arylhydrazononitriles 4a, b with hydroxylamine afforded an amidoximes 9a, b that could be cyclized into 1,2,3-triazole-4-amines 10a, b. In addition, 4a, b could be converted into 4-aminopyrazoles 12a, b via condensation with chloroacetonitrile in the presence of triethylamine as a basic catalyst. Finally, compounds 12a, b were refluxed with dimethylformamide dimethylacetal (DMFDMA) to afford amidines 13a, b that were readily cyclized to the corresponding pyrazolo[4,3-d]pyrimidines 14a, b when refluxed with ammonium acetate.