Direct C-H functionalisation of azoles via Minisci reactions

Azoles have widespread applications in medicinal chemistry; for example, thiazoles, imidazoles, benzimidazoles, isoxazoles, tetrazoles and triazoles appear in the top 25 most frequently used N-heterocycles in FDA-approved drugs. Efficient routes for the late-stage C-H functionalisation of azole cores would therefore be highly desirable. The Minisci reaction, a nucleophilic radical addition reaction onto N-heterocyclic bases, is a direct C-H functionalisation reaction that has the potential to be a powerful method for C-H functionalisations of azole scaffolds. However, azoles have not been as widely studied as substrates for modern Minisci-type reactions as they are often more electron-rich and thus more challenging substrates compared to electron-poor 6-membered N-heterocycles such as quinolines, pyrazines and pyridines typically used in Minisci reactions. Nevertheless, with the prevalence of azole scaffolds in drug design, the Minisci reaction has the potential to be a transformative tool for late-stage C-H functionalisations to efficiently access decorated azole motifs. This review thus aims to give an overview of the C-H functionalisation of azoles via Minisci-type reactions, highlighting recent progress, existing limitations and potential areas for growth.

A Novel PIFA/KOH Promoted Approach to Synthesize C2-arylacylated Benzothiazoles as Potential Drug Scaffolds

To discover an efficient and convenient method to synthesize C2-arylacylated benzothiazoles as potential drug scaffolds, a novel [bis(trifluoroacetoxy)iodo]benzene(PIFA)/KOH synergistically promoted direct ring-opening C2-arylacylation reaction of 2H-benzothiazoles with aryl methyl ketones has been developed. Various substrates were tolerated under optimized conditions affording the C2-arylacylation products in 70-95% yields for 38 examples. A plausible mechanism was also proposed based on a series of controlled experiments.

Visible-light-promoted photocatalyst-free alkylation and acylation of benzothiazoles

Herein we report a protocol for the visible-light-mediated alkylation/acylation reaction of benzothiazoles. Alkyl/acyl substituted Hantzsch esters are easily prepared and rationally used as radical precursors. In the presence of BF3·Et2O and Na2S2O8, various benzothiazole derivatives were readily obtained in good yields. Our user-friendly protocol can proceed by simple irradiation with blue LEDs (λ = 465 nm) and without the assistance of external photocatalysts. The reaction is also characterized by mild conditions and scalability, thus offering an alternative and efficient tool for the synthesis of 2-functionalized benzothiazoles.

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