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

Abstract

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.