An "on water" palladium-catalyzed direct (hetero)arylation of 2H-pyrazolo[3,4-b]pyridines has been developed. The reactions proceeds smoothly with at low catalytic loading at low temperature providing the C3 (hetero)arylated products in good to excellent isolated yields. Free NH 3-arylated 7-azaindazoles were also prepared by simple cleavage of the N-protected groups.
Direct C3-arylation of 1H-pyrazolo[4,3-b]pyridines and direct C3-arylation of 2H-pyrazolo[4,3-b]pyridines in water has been developed. A new protocol for a sequential C3-arylation procedure on a mixture of 1H-and 2H-pyrazolo[4,3b]pyridines followed by in situ PMB cleavage has also been achieved. This procedure led to unprotected (NH) C3-arylated 1Hpyrazolo[4,3-b]pyridines in good yields.
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