Functionalization of indazoles by means of transition metal-catalyzed cross-coupling reactions

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

“…It is even necessary to develop specific conditions for each positional isomer. For example, in the case of indazoles and azaindazoles, the arylation of the 2 H isomer does not require the use of a ligand in contrast to the 1 H isomer because of the lack of the reactivity of the 1 H series compared to the 2 H series. − …”

Palladium‐Catalyzed Oxidative Arylation of 1H‐Indazoles with Arenes

“…Based on previous mechanistic studies, [1,12,25] a plausible mechanism is proposed for this reaction in Scheme 2. First, the starting material 1-methyl-7-nitro-1H-indazole 1 coordinates with the catalyst, formed in situ from Pd(OAc) 2 and 1,10-phenanthroline, to assemble the Intermediate 1.…”

“…In many natural products, pharmaceuticals, functional materials, and biologically active compounds, arylated 1 H ‐indazoles are paramount motifs. [ 1 ] The construction of C–C bonds, which links indazole with arenes and heteroarenes, was ordinarily achieved by transition‐metal‐catalyzed reactions such as Suzuki–Miyaura, [ 2 ] Heck, [ 3 ] Sonogashira, [ 4 ] Stille, [ 5 ] and Negishi. [ 6 ] Since these methods use arylboronic acids, aryl halides, or other aryl organometallic compounds, they are less atom economical and less green than more recently developed C–H activation methods (Equation 1, Scheme 1).…”

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.…”