Electroreductive heterocyclization of ortho-piperidino substituted nitro(het)arenes

Iodine(III)-Catalyzed Oxidative Cyclization of Aryl Amines to Construct N-Alkylbenzimidazoles

An I(III)-catalyzed oxidative cyclization reaction using selectfluor as the oxidant was developed that converts ortho-substituted anilines to benzimidazoles. The mild reaction requires as little as 0.5 mol % of iodobenzene, and its scope is broad: electron-withdrawing or electron-releasing groups on the aniline portion are tolerated, and cyclic or acyclic N-alkylamines are permitted as ortho-substituents. Preliminary mechanistic investigations suggest that benzimidazole formation occurs via cationic reactive intermediates, and an intramolecular kinetic isotope effect of 1.98 ± 0.05 was measured.

Nitroarenes and nitroalkenes as potential amino sources for the synthesis of N-heterocycles

Nitro-compounds are one of the cheapest and most readily available materials in the chemical industry and are commonly utilized as versatile building blocks. Previously, the synthesis of N-heterocycles was largely based on anilines. The utilization of nitroarenes and nitroalkenes for the synthesis of N-heterocyclic compounds can save at least one step, however, as compared to anilines. Thus, considerable attention has been paid to nitroarenes and nitroalkenes as new potential amino sources. Significant progress has been made in the reductive cyclization of nitroarenes or nitroalkenes to access various N-heterocycles in recent years. Herein, we comprehensively summarize the recent progress in the construction of N-heterocycles using nitroarenes and nitroalkenes as potential amino sources. The compatibility of the reaction substrate, its mechanism, applications, advantages, and limitations in this field are also discussed in detail.

Recent Advances to Mediate Reductive Processes of Nitroarenes Using Single-Electron Transfer, Organomagnesium, or Organozinc Reagents

Nitroarenes are readily available compounds that are commonly utilized in reductive processes to form C–NAr bonds via reactive nitrogen intermediates. Recent advances in the development of reductive reactions of nitroarenes using organomagnesium, organozinc, and single-electron transfer reagents are discussed within this short review.

1 Introduction

2 Organomagnesium-Mediated Reductive Reactions of Nitroarenes

3 Organozinc- and Zinc-Mediated Reductive Reactions of Nitroarenes

4 Iodine-Catalyzed Redox Cyclizations of Nitroarenes

5 Titanium(III)-Mediated Reductive Cyclizations

6 Sulfur-Mediated Reductive Reactions of Nitroarenes

7 Alkoxide-Mediated Reductive Reactions of Nitroarenes

8 4,4′-Bipyridine-Mediated Reductive Reactions of Nitroarenes

9 Visible-Light-Driven Reductive Amination Reactions

10 Electrochemical Reductive Reactions

11 Conclusion

Advances in the Synthesis of Ring-Fused Benzimidazoles and Imidazobenzimidazoles

This review article provides a perspective on the synthesis of alicyclic and heterocyclic ring-fused benzimidazoles, imidazo[4,5-f]benzimidazoles, and imidazo[5,4-f]benzimidazoles. These heterocycles have a plethora of biological activities with the iminoquinone and quinone derivatives displaying potent bioreductive antitumor activity. Synthesis is categorized according to the cyclization reaction and mechanisms are detailed. Nitrobenzene reduction, cyclization of aryl amidines, lactams and isothiocyanates are described. Protocols include condensation, cross-dehydrogenative coupling with transition metal catalysis, annulation onto benzimidazole, often using CuI-catalysis, and radical cyclization with homolytic aromatic substitution. Many oxidative transformations are under metal-free conditions, including using thermal, photochemical, and electrochemical methods. Syntheses of diazole analogues of mitomycin C derivatives are described. Traditional oxidations of o-(cycloamino)anilines using peroxides in acid via the t-amino effect remain popular.