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

Abstract

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.

Palladium‐Catalyzed Regioselective C−H Arylation of 4‐Azaindazole at C3, C5 and C7 Positions

“…More interestingly, this method in combination with others from the literature [29,30] could enable the synthesis of C3, C5, C7 triarylated azaindazoles by…”

“…More interestingly, this method in combination with others from the literature [29,30] could enable the synthesis of C3, C5, C7 triarylated azaindazoles by successive regioselective C−H activation. In preliminary screens, the C3 arylation was investigated from the C5, C7‐disubstituted azaindazole N ‐oxide 7 a with 1‐iodo‐4‐methoxybenzene using selective reported experimental conditions [Pd(PPh 3 ) 4 , phen, Ag 2 CO 3 , H 2 O, 24 h, 100 °C] [29,30] . As obtained by the theoretical calculations (vide supra), the deactivation at C3 position by the N ‐oxide inhibits the reaction and only the starting material 7 a was recovered.…”

Recent Advances and Prospects of Organic Reactions “On Water”

“…Another palladium‐ catalysed direct C3‐ arylation of 1 H ‐ and 2 H ‐Pyrazolo[4,3‐ b ]pyridines on water was reported (Scheme , Scheme ) . Various iodoaryls and iodo‐heteroaryls were reacted with 1 H ‐ and 2 H ‐Pyrazolo[4,3‐ b ]pyridines to afford the corresponding C3‐ arylated products in moderate to excellent yields.…”

A regioselective C7 bromination and C7 palladium-catalyzed Suzuki–Miyaura cross-coupling arylation of 4-substituted NH-free indazoles

“…Recently, our group and others were actively involved in the functionalization of NH-free or protected 1H and 2H-indazoles. Despite the recent advances made in this eld, namely the direct C3 and C7-arylations 32,[49][50][51] and the Suzuki-Miyaura coupling at C3, C4, C5 and C6 positions, 31,[52][53][54] to date, no example of selective arylation of NH-free or protected indazoles using Suzuki-Miyaura process, has been described at the C7 position. It is important to note that we previously reported only two examples of C7 direct arylation of indazoles containing a C4 nitro group in which C3 position was already substituted with a phenyl group.…”