2-Aminobenzimidazoles in Organic Syntheses

2-Aminobenzimidazole is a readily available chemical and can also be prepared easily in the laboratory. The present review highlights different methods to prepare various 2-aminobenzimidazoles. The utility of this organic synthon in preparing a wide variety of substituted benzimidazoles and benzimidazole heterocycles is systematically discussed and the application of such compounds in the development of new chemotherapeutic agents are included. 1 Introduction 2. Synthesis of 2-Aminobenzimidazoles 2.1. From o-Phenylenediamines 2.2. From o-Substituted Nitrobenzenes 2.3. From Phenylhydrazines 2.4. From Thioureas 2.5 From Benzimidazoles 3. Substitution Reactions 3.1. Alkylation and Arylation Reactions 3.2 Acylation and Aroylation Reactions 3.3. Sulphonylation Reactions 4. Substitutions Involving Heterocyclisation 5. Electrophilic Reactions 6. Reaction with Isothiocyanates and Isocyanates 7. Reaction with Carbonyl Compounds 8. Reaction with Nitriles 9. Reaction with Alkenes and Alkynes 10. Coupling Reactions 11. Miscellaneous Reactions 12. 2-Aminobenzimidazoles in Pharmaceutical and Industrial Chemistry 13. Conclusions