A novel, convenient and efficient protocol for the construction of various 2-aminophenyl benzothiazoles by domino intra- and intermolecular C–N cross-coupling reactions of arylisothioureas with aryl iodides using an inexpensive, air stable and readily available copper catalyst is described. The arylisothioureas were obtained from thiourea via copper promoted desulfurization followed by nucleophilic substitution. In addition, the reactivity of arylhalides and the reaction mechanism have also been studied. The protocol features operational simplicity and a broad substrate scope.

The synthesis of 2-(5-methyl-2-nitrophenyl)-5-(substituted)-1,3,4-oxadiazoles (5a–e) and thiadiazoles (6a–e) was carried out by refluxing of N-(5-methyl-2-nitrobenzoyl)-2-substituted carbohydrazide with phosphorous oxychloride and Lawesson’s reagent respectively. The N-(5-methyl-2-nitrobenzoyl)-2-substituted carbohydrazides was synthesized by treating 2(5-methyl-2-nitrobenzohydrazide) with various aryl acids in the presence of HATU and DIPEA. Compounds 6a, 5c and 5d exhibited significant cytotoxic properties when compared to standard podophyllotoxin. Further, the compounds were also studied for their antibacterial activities.

A series of 3-aryl indazoles and 1-methyl-3-aryl indazole derivatives are prepared with exceptional yields by coupling with several arylboronic acids and methylation by two dissimilar approaches. The as-prepared indazole derivatives (3a–3j) and their N-methyl derivatives (5a–5j) are evaluated for in vitro anticancer activity against two cancer cell lines, HCT-116 and MDA-MB-231. The results reveal that the indazole derivatives tested display mild to moderate anticancer activities against the cell lines tested.

A facile, one-pot, and proficient method was developed for the production of various 2-arylaminobenzimidazoles. This methodology is based for the first time on a copper catalyst promoted domino C–N cross-coupling reaction for the generation of 2-arylaminobenzimidazoles. Mechanistic investigations revealed that the synthetic pathway involves a copper-based desulphurization/nucleophilic substitution and a subsequent domino intra and intermolecular C–N cross-coupling reactions. Some of the issues typically encountered during the synthesis of 2-arylaminobezimidazoles, including the use of expensive catalytic systems and the low reactivity of bromo precursors, were addressed using this newly developed copper-catalyzed method. The reaction procedure is simple, generally with excellent substrate tolerance, and provides good to high yields of the desired products.

Research on heterocyclic compounds is an area of continuous focus, capturing the interest of both synthetic and natural product chemists. Indazoles are one of the rare heterocycles that are available in nature. Indazole and its derivatives are one of the most important classes of heterocycles in pharmacological molecules. The structurally different indazole motifs, with impressive bioactivity, have drawn increasing attention from medicinal chemists in recent years for the continuous development of novel drug moieties. Thus, knowledge of the biological activities and synthetic pathways of indazole scaffolds is essential to enhancing further developments in the number of indazole-based lead molecules. The goal of the present review is to highlight information on the biological properties of some existing indazole-based drugs and activities of novel bioactive indazole compounds in clinical trails, with specific attention to the most recent advances in various synthetic strategies towards indazole and its derivatives over the past 7 years (2017–2024). Moreover, we discuss the substrate tolerance and mechanistic insights for most of the summarized synthetic protocols. Graphical Abstract