Synthesis and structure of some azolo[a]pyrimidines, 2,6,7,8-tetrahydro-1H-cyclopenta[e]azolo[a]pyrimidines, 6,7-dihydro-5H-cyclopenta[f]azolo[a]pyrimidines, 7,8-dihydro-6H-cyclopenta[f]-s-triazolo[4,3-b]pyridazine, 5,6,7,8-tetrahydro-azolo[b]quinazolines, 6,7,8,9-tetrahydroazolo[a]quinazolines, and 7,8,9,10-tetrahydro-s-triazolo[3,4-a]phthalazine

The condensation of 3-amino-1,2,4-triazole (2), its 3-methyl (7) and 5-methylthio (23) derivatives, 3-aminopyrazole (10) and its 4-cyano-derivative (27), 4-amino-1,2,4-triazole (13). 5-aminotetrazole (16), and 2-aminobenzimidazole (33) with 4,4-dimethoxybutan-2-one (1), 2-hydroxymethylenecyclohexanone (20), and 2-hydroxymethylenecyclopentanone (35) has been investigated. 7-Methyltetrazolo[1,5-a]pyrimidine (18) and not, as formerly claimed, 5-methyltetrazolo[1,5-a]pyrimidine (17) is shown to be the final product in the reaction of 5-aminotetrazole (16) and 4,4-dimethoxybutan-2-one (1). Most of the aminoazoles on condensation with the β-ketoacetal (1) or the β-ketoaldehyde (20) give mixtures of both possible fusion products, whereas the reaction of these aminoazoles with the β-ketoaldehyde (35) affords, in the main, angularly fused products. The linearly and angularly fused products are distinguished by 1H n.m.r. And 13C n.m.r. Spectroscopy and independent synthesis. These same condensation products are again observed during the reactions between the aminoazoles and the β-ketoanils, 2-(2-acetylvinylamino)pyridine (40), 2-(2-pyridylaminomethylene)cyclohexanone (42), and 2-(2-pyridylaminomethylene)cyclopentanone (43). The mechanism of these condensation reactions is also discussed.