Halogen dance in pyrazole 1-oxides: synthesis of pyrazolo[3,4-c]quinoline 1-oxides

The synthesis of a new series of 3-substituted pyrazolo[3,4-c]quinoline 1-oxides is presented. Regioselective bromine–magnesium exchange of 2-benzylated 3,4,5-tribromopyrazole 1-oxides and subsequent halogen dance of the resulting monometalated intermediates was used to synthesize fused pyrazoloquinoline 1-oxides.