Palladium-Catalyzed C3-Arylations of 1 H- and 2 H-Pyrazolo[4,3- b]pyridines on Water.

Direct C3-arylation of 1 H-pyrazolo[4,3- b]pyridines and direct C3-arylation of 2 H-pyrazolo[4,3- b]pyridines in water has been developed. A new protocol for a sequential C3-arylation procedure on a mixture of 1 H- and 2 H-pyrazolo[4,3- b]pyridines followed by in situ PMB cleavage has also been achieved. This procedure led to unprotected ( NH) C3-arylated 1 H-pyrazolo[4,3- b]pyridines in good yields.