## 1 Introduction
Generally speaking, chemical functionalization of indazole usually demands a catalyst, along with an appropriate solvent, temperature, and reaction time, meaning that future large-scale production would involve many economic and environmental issues. The C-functionalization carried out on C-3 position of \(1H\)-indazole played a key role in promoting the pharmaceutical activity of indazole derivatives. For example, the abnormal ignition (phosphorylation) of unc-51-like kinase 1 (ULK1), a ubiquitously expressed protein activated by stress-induced autophagy under many conditions, decreases the efficiency of the current chemotherapeutics for cancer, and meanwhile increases the growth of cancer [16]. Therefore, using small molecule inhibitors of ULK1 such as SR-17398 (Figure 1c) could block the phosphorylation of ULK1 and simultaneously enhance the effect of chemotherapy [17]. The backbone of SR-17398 is indazole, whose nitrogen-containing heterocyclic structure can deform the configuration of ULK1, finally blocking the activation of ULK1 [18]. However, if the C-3 position of indazole on SR-17398 is functionalized by introducing a 1-naphthyling group (Figure 1d), the half inhibitory concentration (IC\({}_{50}\)) is greatly decreased, and the C-3 position of indazole showed an influence on the inhibitory deformation of ULK1 [18]. On the other hand, C-3 functionalized \(2H\)-indazole also showed high activity for the treatment of neurological diseases (Figure 1e) [19]. Functionalization of C-3 of indazoles allows developing new and powerful pharmaceuticals. In practice, direct functionalization of C-3 on \(1H\)-indazole suffers from several drawbacks. First, direct C-3 alkylation of \(1H\)-indazole through the Minisci reaction (addition of nucleophilic carbon radical to protonated electron-deficient aromatic heterocyclic) produced a very low yield, which can be ascribed to the unique electronic structure of the five-membered nitrogen-containing heterocyclic [20]. Next, direct C-3 ylation of \(1H\)-indazole required an uncommon catalyst and challenging reaction conditions [4]. These results delay progress to large-scale production. All in all, in view of the present progress in C-3 functionalization, exploring new synthetic methods deserves more attention. The Suzuki-Miyaura cross-coupling reaction represents a palladium (Pd)-catalyzed C-C bond formation, already standing as a powerful methodology for the construction of sophisticated molecules for the last two decades [21; 22]. First of all, taking into account the mechanism of Pd-catalyzed Suzuki-Miyaura coupling of aryl halide with organoboronic acid, a Pd\({}^{(0)}\) to Pd\({}^{(\text{II})}\) cycle is widely accepted as the most reasonable pathway [22]. In detail, the oxidative addition of aryl halide to Pd\({}^{(0)}\) generates a Pd\({}^{(\text{II})}\) intermediate, while the transmetalation of the Pd\({}^{(\text{II})}\) intermediate, followed by the reductive elimination, produces the coupled product and regenerates the active Pd\({}^{(0)}\)[22; 23]. Next, Pd-catalyzed Suzuki-Miyaura coupling has shown several significant advantages, particularly regarding its broad functional group tolerance and mild reaction conditions [24; 25]. For instance, the suitable electrophiles cover sterically congested molecules, inert aryl, and vinyl chlorides, as well as sulfonate derivatives, while the nucleophiles also include thermally unstable polyfluorophenyl and 2-heteroaryl boron reagents [25]. Meanwhile, the organoboron compounds (electrophile) exhibit high stabilities towards air and moisture [24]. Therefore, although \(1H\)-indazole has a sophisticated nitrogen-containing heterocyclic, it is promising to develop Pd-catalyzed Suzuki-Miyaura coupling reaction for C-3 functionalization of \(1H\)-indazole. On the other hand, the recovery and recycling of Pd catalysts has not been well addressed. Herein, depending on the catalyst precursor, the known Pd catalytic systems can be divided into homogeneous and heterogeneous systems.