Pyrazolo[3,4-b]pyridines. The preparation of 1-protected-1H-pyrazolo[3,4-b]pyridines and attempts to remove the 1-substituent. Some reactions of 1-benzyl-1H-pyrazolo[3,4-b]pyridine and its 7-oxide

Abstract

1-Protected-1H-pyrazolo[3,4-b]pyridines [e.g. (4)] and -1H-pyrazolo[3,4-b]pyridin-6(7H)-ones [e.g. (14)] have been obtained from 1-substituted-5-aminopyrazoles [e.g. (1)], and the removal of the protecting groups has been investigated. Cyclisation of 1-substituted-5-aminopyrazoles with ethyl acetoacetate under acidic conditions or of the β3-aminopropionic acid derivative (19) under the same conditions gave only the 1H-pyrazolo[3,4-b]pyridin-6(7H)-one isomer [e.g. (14) and (20), respectively]. N-Oxidation of 1-benzyl-1H-pyrazolo[3,4-b]pyridine (4) gave the 7-oxide (21) which yielded (20) and the less usual β-substitution product (22) with acetic anhydride. Nitration of either (4) or (21) gave only substitution at the para-position of the 1 -benzyl substituent, but bromination or chlorination gave substitution at the 3-position of the heterocycle.