A Facile C‐H Insertion Strategy using Combination of HFIP and Isocyanides: Metal‐Free Access to Azole Derivatives

Recent Advances in the Development of Greener Methodologies for the Synthesis of Benzothiazoles

The benzothiazole ring system has been recognised with crucial pharmacophoric features being present among various approved drugs and clinical and pre-clinical candidates. The medicinal importance of this privileged scaffold stimulated the interest of synthetic medicinal/ organic chemists for the synthesis of its derivatives due to their diverse biological applications. In most of the reports in the literature, benzothiazoles were synthesized by cyclocondensation of 2- aminothiophenol with either carboxylic acid and its derivatives or aldehydes. However, many of these procedures involve reaction conditions that are not in conformity with sustainable chemistry development. The negative impact of chemicals and their manufacturing processes on the environment, human health, and biodiversity raises safety concerns. On the other hand, the utilization of non-renewable energy sources, use of rare earth metals as catalysts, involvement of costly chemicals, prolonged reaction time at high temperatures, and considerable waste generation diminish the greener impact of these reaction methodologies and make them non-sustainable. In order to avoid such drawbacks of the non-sustainable practices in the synthesis of benzothiazoles, there have been continuous efforts to develop greener methodologies for the construction of this bioactive scaffold. This review aims to delve into the literature reports on the recent advancements in the development of greener methodologies for the synthesis of bioactive benzothiazoles.

Thermal and Photoinduced Radical Cascade Annulation using Aryl Isonitriles: An Approach to Quinoline-Derived Benzophosphole Oxides

Herein, we present a radical cascade addition cyclization sequence to access quinoline-based benzophosphole oxides from ortho-alkynylated aromatic phosphine oxides using various aryl isonitriles as radical acceptors and inexpensive tert-butyl-hydroperoxide (TBHP) as a terminal oxidant in the presence of a catalytic amount of silver acetate. Alternatively, the same cascade can be realized through a sustainable photochemical approach utilizing 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as an organic photocatalyst at room temperature. The introduced modular approach shows broad functional group tolerance and offers straightforward access to complex P,N-containing polyheterocyclic arenes. These novel π-extended benzophosphole oxides exhibit interesting photophysical and electrochemical properties such as absorption in the visible region, emission and reversible reduction at low potentials, which makes them promising for potential materials science applications. The photophysical properties can further be tuned by the addition of external Lewis and Brønsted acids.

Biomedical applications of selective metal complexes of indole, benzimidazole, benzothiazole and benzoxazole: A review (From 2015 to 2022)

Indole, benzoxazole benzothiazole and benzimidazole are excellent classes of organic heterocyclic compounds. These compounds show significant application in pharmacy, industries, dyes, medicine, polymers and food packages. These compounds also form metal complexes with copper, zinc, cadmium, nickel, cobalt, platinum, gold, palladium chromium, silver, iron, and other metals that have shown to be significant applications. Recently, researchers have attracted enormous attention toward heterocyclic compounds such as indole, benzimidazole, benzothiazole, benzoxazole, and their complexes due to their excellent medicinal applications such as anti-ulcerogenic, anti-cancer, antihypertensive, antifungal, anti-inflammatory, antitubercular, antiparasitic, anti-obesity, antimalarial, antiglycation, antiviral potency, antineuropathic, analgesic antioxidant, antihistaminic, and antibacterial potentials. In this article, we summarize the medicinal applications of these compounds as well as their metal complexes. We hope this article will help researchers in designing and synthesizing novel and potent compounds with significant applications in various fields.

Triple-Consecutive Isocyanide Insertions with Aldehydes: Synthesis of 4-Cyanooxazoles

An efficient TMSOTf-promoted selective triple consecutive insertions of tert-butyl isocyanide into aldehydes has been developed, affording pharmacological interesting 4-cyanooxazoles in high yields in a one pot manner. The given method encompasses a wide range of substrates with tert-butyl isocyanide serving as sources of critical "CN" and "C-N═C" moieties. The versatile transformations of the resulting 4-cyanooxazoles were demonstrated. The key reaction intermediates for plausible mechanisms were determined.

Transition-Metal-Free Transfer Hydrogenative Cascade Reaction of Nitroarenes with Amines/Alcohols: Redox-Economical Access to Benzimidazoles

This report describes an efficient transition-metal-free process toward the transfer hydrogenative cascade reaction between nitroarenes and amines or alcohols. The developed redox-economical approach was realized using a combination of KO^tBu and Et₃SiH as reagents, which allows the synthesis of benzimidazole derivatives via σ-bond metathesis. The reaction conditions hold well over a wide range of substrates embedded with diverse functional groups to deliver the desired products in good to excellent yields. The mechanistic proposal has been depicted on the basis of a series of control experiments, mass spectroscopic evidence which is well supported by density functional theory (DFT) calculations with a feasible energy profile.