A convenient route for the synthesis of pyrazolo[3,4-<i>d</i>]pyrimidine, pyrazolo[3,4-<i>b</i>][1,6]naphthyridine and pyrazolo[3,4-<i>b</i>]quinoline derivatives

Abstract

Friedländer condensation of 5-aminopyrazole-4-carbaldehydes 1 with formamide 2a or benzamide 2b gave pyrazolo[3,4-d]pyrimidine derivatives 3. Cyclocondensation of 1 with cyclopentanone, N-benzyl-4-piperidone and 6-methoxy-1-tetralone yielded cyclopenta[b]pyrazolo[4,3-e]pyridines 4, pyrazolo[3,4-b]-[1,6]naphthyridines 5 and benzo[h]pyrazolo[3,4-b]quinolines 6, respectively. Analogous condensation of cyclohexanone 7a or 2-methyl-1-cyclohexanone 7b with 1 afforded pyrazolo[3,4-b]quinoline derivatives 8a-d. Heating 1 with dimedone furnished pyrazolo[3,4-b]quinolinone derivatives 9. Vilsmeier-Haack formylation of 9 yielded a mixture of two compounds 10 and 11. Further bispyrazolo[3,4-b:4,3-f]-quinolines 12a, b were obtained on cyclocondensation of 11a, b with phenyl hydrazine.