Synthesis of 2-Arylbenzothiazole and 2-Arylthiazole Derivatives via a Ru-Catalyzed meta-Selective C–H Nitration Reaction

Regiodivergent Metal-Catalyzed Oxidative Alkynylation of 2-Arylthiazoles with Terminal Alkynes under Air Conditions

Regiodivergent transition-metal-catalyzed oxidative C5- and ortho-alkynylation of 2-arylthiazoles have been demonstrated. Namely, Pd(II)-catalysis selectively generated C5-alkynylated products from the reaction of 2-arylthiazoles and terminal alkynes. In contrast, Ru(II)-catalysis exclusively provided ortho-alkynylated products from the same substrates. This protocol features a wide substrate scope, good functional group tolerance, high atom-economy, and exclusive regioselectivity. The alkynylated products can be readily converted into highly valuable synthons, which hold potential for applications in the fields of medicinal chemistry and materials science.

Regiodivergent C-H alkynylation of 2-arylthiazoles switched by RuII and PdII catalysis

Two complementary regiodivergent C-H alkynylations of 2-arylthiazoles are reported. When RuII catalysis is employed, an aryl ortho-alkynylation process is favored. The alkynylated products are gained in good yields. With the use of PdII catalysis, a thiazole C5-alkynylation process is developed, allowing for the construction of C5-alkynylated products. This strategy not only expands the methods for the functionalization of 2-arylthiazoles, but also provides new opportunities for the rapid assembly of complex molecular structures, which may have great potential in organic synthesis, medicinal chemistry, and materials science.

Nitration of Pyrrolo[2,1-a]isoquinolines

We have successfully modified a series of pyrrolo[2,1-a]isoquinolines via direct nitration under mild reaction conditions. Easily accessible nitrates including CAN, Cu(NO₃)₂·H₂O, and Fe(NO₃)₃·9H₂O all can serve as effective nitrating reagents for functionalizing pyrrolo[2,1-a]isoquinolines. Various nitro-bearing pyrrolo[2,1-a]isoquinolines have been efficiently prepared in acceptable to good yields.

Mn(III)-Mediated Radical Addition/Cyclization of Isocyanides with Aryl Boronic Acids/Diarylphosphine Oxides: Access to 11-Functionalized Dibenzodiazepines

A Mn(III)-mediated radical addition/cyclization reaction of isocyanides with aryl boronic acids/diarylphosphine oxides has been developed. A series of 11-arylated/-phosphorylated dibenzodiazepines were efficiently constructed in moderate to excellent yields under mild reaction conditions via imidoyl radical process. The present protocol offers novel access to functionalized seven-membered N-heterocycles.

meta-Allylation of Arenes via Ruthenium-Catalyzed Cross-Dehydrogenative Coupling

A successful example of oxidative meta-dehydrogenative allylation of arenes with alkenes has been developed using Ru(PPh₃)₃Cl₂ as a catalyst and DTBP as an oxidant. In the allylation process, pyrimidines, pyrazoles, and purines, found widely in nucleosides, were effective auxiliary groups. Gram-scale experiments took place smoothly under optimized conditions. Mechanistic studies indicated that ruthenium-catalyzed meta-dehydrogenative allylation was a free-radical process. The allylation process developed herein provides an efficient and practical strategy to prepare versatile meta-allylated arenes.

Acid-Free Copper-Catalyzed Electrophilic Nitration of Electron-Rich Arenes with Guanidine Nitrate

A practical copper-catalyzed nitration of electron-rich arenes with trimethylsilyl chloride and guanidine nitrate is reported. A variety of nitrated products were generated in moderate to excellent yields (32-99%) at ambient temperature under acid-free, open-flask, and operationally simple conditions.

Recent progress in the nitration of arenes and alkenes

Nitro compounds are a predominant class of synthetic intermediates and building blocks for the preparation of a wide range of nitrogen-containing compounds in the chemical industry. As such, impressive progress has been currently made in the nitration of aromatics and olefins with excellent functional group tolerance and site-selectivity. In this mini review, we intend to highlight the regiospecific nitration of arenes and alkenes in various reaction systems. The involved mechanisms are discussed as well.

Remote C–H Functionalizations by Ruthenium Catalysis

Synthetic transformations of otherwise inert C–H bonds have emerged as a powerful tool for molecular modifications during the last decades, with broad applications towards pharmaceuticals, material sciences, and crop protection. Consistently, a key challenge in C–H activation chemistry is the full control of site-selectivity. In addition to substrate control through steric hindrance or kinetic acidity of C–H bonds, one important approach for the site-selective C–H transformation of arenes is the use of chelation-assistance through directing groups, therefore leading to proximity-induced ortho-C–H metalation. In contrast, more challenging remote C–H activations at the meta- or para-positions continue to be scarce. Within this review, we demonstrate the distinct character of ruthenium catalysis for remote C–H activations until March 2021, highlighting among others late-stage modifications of bio-relevant molecules. Moreover, we discuss important mechanistic insights by experiments and computation, illustrating the key importance of carboxylate-assisted C–H activation with ruthenium(II) complexes.

1 Introduction

2 Stoichiometric Remote C–H Functionalizations

3 meta-C–H Functionalizations

4 para-C–H Functionalizations

5 meta-/ortho-C–H Difunctionalizations

6 Conclusions

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

Recent advances in nitro-involved radical reactions

Significant progress in the chemistry of nitro radicals has been witnessed in the past decades, providing efficient and rapid access to nitro-containing compounds. This review describes recent advances in nitro-involved radical reactions, and summarizes various transformations.