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.

Direct and site‐selective C5 and C7 palladium‐catalyzed C−H arylations of 4‐azaindazole N‐oxide have been achieved. A bidentate ligand and Pd(OAc)2 catalyst in toluene promoted the activation of C5 position, while a phosphine ligand and PdCl2 catalyst in DMA directed the arylation at C7 position. Using this new method, the synthesis of C5, C7‐diarylated 4‐azaindazole N‐oxides as well as the C3, C5, C7‐triarylated 4‐azaindazoles was achieved towards future medicinal compounds development.

The regioselective C-H functionalization of the five-membered ring of the 6,5-fused heterocyclic systems is nowadays well documented due to its high reactivity compared to the six-membered ring. So, developing new procedures of C-H functionalization of the six-membered ring “by thinking out of the box” is extremely challenging, which explains the limited number of reports published to date. This review paper aims to highlight advances achieved in this emerging chemistry research and discusses recently reported methods.

The front cover picture, designed by El Kazzouli and co‐workers, illustrates the site‐selective C5 and C7 palladium‐catalyzed C‐H arylations of 4‐azaindazole N‐oxide. The 1,10‐phenanthroline as ligand and Pd(OAc)2 as catalyst in toluene promoted the activation of C5 position, while the triphenyl phosphine as ligand and PdCl2 as catalyst in DMA directed the arylation at C7 position. This new method allows the synthesis of C5, C7‐diarylated 4‐azaindazole N‐oxides as well as the C3, C5, C7‐triarylated 4‐azaindazoles. Details can be found in the Communication by El Kazzouli, Suzenet, Guillaumet and co‐workers (S. Faarasse, S. El Kazzouli, O. Bourzikat, S. Bourg, S. Aci‐Sèche, P. Bonnet, F. Suzenet, G. Guillaumet Adv. Synth. Catal. 2021, 363, 3937–3945; DOI: 10.1002/adsc.202001421).