Synthesis of Benzothiazoles through Copper-Catalyzed One-Pot Three-Component Reactions with Use of Sodium Hydrosulfide as a Sulfur Surrogate

Iron(III)-Catalyzed Regioselective Synthesis of Electron-Rich Benzothiazoles from Aryl Isothiocyanates via C-H Functionalization

We report herein a direct synthetic route for the preparation of 2-arylbenzothiazoles using aryl isothiocyanates and electron-rich arenes. The synthetic route involves triflic acid promoted addition of the arenes to aryl isothiocyanates followed by FeCl₃-catalyzed C-S bond formation via C-H functionalization. The approach provides the advantage of synthesis of benzothiazoles without the conventional use of aryl aldehyde/carboxylic acid precursors employing the less expensive iron(III) catalyst.

A convenient synthesis of N-(hetero)arylamides by the oxidative coupling of methylheteroarenes with amines

An oxidative amidation of 2-methylpyridines/2-methylbenzimidazole with amines using copper acetate and elemental sulfur in DMSO to afford various N-(hetero)arylamides has been accomplished. Mechanistic studies reveal the intermediacy of N-(pyridin-2-ylmethyl)aniline and confirm the role of DMSO as the oxygen source.

Metal-catalyzed C-S bond formation using sulfur surrogates

Sulfur-containing compounds are present in a wide range of biologically important natural products, drugs, catalysts, and ligands and they have wide applications in material chemistry. Transition metal-catalyzed C-S bond-forming reactions have successfully overcome the obstacles associated with traditional organosulfur compound syntheses such as stoichiometric use of metal-catalysts, catalyst-poisoning and harsh reaction conditions. One of the key demands in metal-catalyzed C-S bond-forming reactions is the use of an appropriate sulfur source due to its odor and availability. The unpleasant odor of many organic sulfur sources might be one of the reasons for the metal-catalyzed C-S bond-forming reactions being less explored compared to other metal-catalyzed C-heteroatom bond-forming reactions. Hence, employing an appropriate sulfur surrogate in the synthesis of organosulfur compounds in metal-catalyzed reactions is still of prime interest for chemists. This review explores the recent advances in C-S bond formation using transition metal-catalyzed cross-coupling reactions and C-H bond functionalization using diverse and commercially available sulfur surrogates. Based on the different transition metal-catalysts, this review has been divided into three major classes namely (1) palladium-catalyzed C-S bond formation, (2) copper-catalyzed C-S bond formation, and (3) other metal-catalyzed C-S bond formation. This review is further arranged based on the different sulfur surrogates. Also, this review provides an insight into the growing opportunities in the construction of complex organosulfur scaffolds covering natural product synthesis and functional materials.

Recent Advances in the Synthesis and Applications of 2-Arylbenzothiazoles

This review firstly covers the applications of 2-arylbenzothiazoles as amyloid imaging agents, antitumor agents, and organic luminescent materials. Then we review the recent advances in the synthesis of 2-arylbenzothiazole derivatives. On the one hand, we introduce the approaches for construction of the 2-arylbenzothiazole core, including the following categories: (i) classic condensation of 2-aminothiophenols, (ii) direct arylation of benzothiazoles, (iii) intramolecular cyclization of thiobenzanilides, and (iv) tandem cyclization of anilines/ nitroarenes­ with elemental sulfur or sulfides. On the other hand, the transition-metal-catalyzed direct C–H functionalizations of 2-aryl­benzothiazoles are also involved in this review.

1 Introduction

2 Applications of 2-Arylbenzothiazoles

3 Construction of the 2-Arylbenzothiazole Core

4 Synthesis 2-Arylbenzothiazoles via Direct C–H Functionalization

5 Conclusion

Current advances in the synthetic strategies of 2-arylbenzothiazole

Benzothiazole is a privileged scaffold in the field of synthetic and medicinal chemistry. Its derivatives and metal complexes possess a gamut of pharmacological properties and high degree of structural diversity that has proven it vital for the investigation for novel therapeutics. The 2nd position of benzothiazole is the most active site that makes 2-arylbenzothiazole as felicitous scaffolds in pharmaceutical chemistry. The extensive significance of benzo-fused heterocyclic moieties formation has led to broad and valuable different approaches for their synthesis. This review deals with the synthetic approaches developed so far for the synthesis of 2-arylbenzothiazoles. Moreover, this article abridges the publications devoted to the synthesis of this moiety over the last 6 years. This study gives a current precis of research on the fabrication of 2-arylbenzothiazoles through different synthetic pathways and shall be helpful for researchers and scientists who are working in this field to make more potent biologically active benzothiazole-based drugs.

Engineered C-S Bond Construction

Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.

Ruthenium-catalyzed decarboxylative C–S cross-coupling of carbonothioate: synthesis of allyl(aryl)sulfide

A novel ruthenium-catalyzed decarboxylative cross-coupling of carbonothioate is disclosed. This method provides straightforward access to the corresponding allyl(aryl)sulfide derivatives in generally good to excellent yields under mild conditions and features a broad substrate scope, wide group tolerance and in particular, no need to use halocarbon precursors.

A method for the construction of a C–S bond via the ruthenium-catalyzed decarboxylative cross-coupling of carbonothioate under mild conditions is described.

Versatile one-pot synthesis of benzo-fused thiacycles by copper catalysis

A series of 2-substituted benzo[e][1,3]thiazines and 2-substituted benzo[b]thiophenes were synthesized using a versatile, simple and efficient copper-catalysed methodology.

N-Heterocyclic carbene copper(i) complex-catalyzed synthesis of 2-aryl benzoxazoles and benzothiazoles

A new an efficient synthesis of 2-aryl benzoxazoles and benzothiazoles by intramolecular cyclization of 2-haloanilides/2-halothioanilides using a copper(i)-NHC complex is described.

Fe–Cu catalyzed synthesis of symmetrical and unsymmetrical diaryl thioethers using 1,3-benzoxazole-2-thiol as a sulfur surrogate

An efficient Fe–Cu catalyzed approach is herein developed using 1,3-benzoxazole-2-thiol as a thiol surrogate for the synthesis of symmetrical and unsymmetrical diaryl thioethers.

Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems

Hydrogen sulfide (H2S), a gaseous species produced by both bacteria and higher eukaryotic organisms, including mammalian vertebrates, has attracted attention in recent years for its contributions to human health and disease. H2S has been proposed as a cytoprotectant and gasotransmitter in many tissue types, including mediating vascular tone in blood vessels as well as neuromodulation in the brain. The molecular mechanisms dictating how H2S affects cellular signaling and other physiological events remain insufficiently understood. Furthermore, the involvement of H2S in metal-binding interactions and formation of related RSS such as sulfane sulfur may contribute to other distinct signaling pathways. Owing to its widespread biological roles and unique chemical properties, H2S is an appealing target for chemical biology approaches to elucidate its production, trafficking, and downstream function. In this context, reaction-based fluorescent probes offer a versatile set of screening tools to visualize H2S pools in living systems. Three main strategies used in molecular probe development for H2S detection include azide and nitro group reduction, nucleophilic attack, and CuS precipitation. Each of these approaches exploits the strong nucleophilicity and reducing potency of H2S to achieve selectivity over other biothiols. In addition, a variety of methods have been developed for the detection of other reactive sulfur species (RSS), including sulfite and bisulfite, as well as sulfane sulfur species and related modifications such as S-nitrosothiols. Access to this growing chemical toolbox of new molecular probes for H2S and related RSS sets the stage for applying these developing technologies to probe reactive sulfur biology in living systems.

One-pot odorless thia-Michael reaction by copper ferrite nanoparticle-catalyzed reaction of elemental sulfur, aryl halides and electron-deficient alkenes

One-pot CuFe₂O₄ catalyzed reaction of aryl halides or boronic acids with sulfur and electron-deficient alkenes for generation of sulfides.

An efficient desulfitative C–C cross coupling of fused thiazolidine-2-thione with boronic acids and boronic acid pinacol esters: formation of fused thiazoles

An efficient Pd(0)-catalyzed Cu(i)-mediated desulfitative C–C cross-coupling of benzo-fused thiazolidine-2-thione with boronic acids under neutral conditions and boronic acid pinacol esters under basic conditions has been demonstrated.

Iron nanotube-silica composite (ZVI-S-PCAT modified silica composite) preparation, characterization and application as a recyclable catalytic system for 5-membered ring organic transformations

The ZVI-S-PCAT modified silica composite is a successful catalytic framework for synthesizing 5-membered heterocylic rings and a future sensor material.

Efficient sodium bisulfite-catalyzed synthesis of benzothiazoles and their potential as ureases inhibitors

In this work we report the successful use of sodium bisulfite as catalyst for the synthesis of 19 benzothiazoles (BZTs) under microwave irradiation with yields from 80% to 100%.

A comparative study between para-aminophenyl and ortho-aminophenyl benzothiazoles using NMR and DFT calculations

Ortho-substituted and para-substituted aminophenyl benzothiazoles were synthesised and characterised using NMR spectroscopy. A comparison of the proton chemical shift values reveals significant differences in the observed chemical shift values for the NH protons indicating the presence of a hydrogen bond in all ortho-substituted compounds as compared to the para compounds. The presence of intramolecular hydrogen bond in the ortho amino substituted aminophenyl benzothiazole forces the molecule to be planar which may be an additional advantage in developing these compounds as Alzheimer's imaging agent because the binding to amyloid fibrils prefers planar compounds. The splitting pattern of the methylene proton next to the amino group also showed significant coupling to the amino proton consistent with the notion of the existence of slow exchange and hydrogen bond in the ortho-substituted compounds. This is further verified by density functional theory calculations which yielded a near planar low energy conformer for all the o-aminophenyl benzothiazoles and displayed a hydrogen bond from the amine proton to the nitrogen of the thiazole ring. A detailed analysis of the (1)H, (13)C and (15)N NMR chemical shifts and density functional theory calculated structures of the compounds are described.