First nucleophilic aromatic substitution of annelated pyrazole.

3-Chloropyrazolo3,4-c]quinoline 5, 3-chloropyrazolo3,4-c]isoquinoline 6, 1,2-dihydro-1,2-dimethylpyrazolo3,4-c]quinolin-3-one 8, and 1,2-dihydro-1,2-dimethylpyrazolo3,4-c]isoquinolin-3-one 10 were obtained by acid-induced nucleophilic aromatic substitution (S(N)H) of H-3 in N-hydroxypyrazolo3,4-c]quinoline 1b and in N-hydroxy pyrazolo3,4-c]isoquinoline 3b. In the acid-induced chlorination, 3b was far more reactive than 1b, whereas the related N-hydroxypyrazolo4,3-c]quinoline 2b and N-hydroxypyrazolo4,3-c]isoquinoline 4b were completely unreactive toward S(N)H under identical conditions.