Catalytic Synthesis of 1,2,4,5-Tetrasubstituted-1H-imidazole Derivatives: State of the Art

Tetrasubstituted 1H‐imidazoles are a large family of heteroarene derivatives that are known to include natural products isolated from marine sponges and synthetic compounds possessing a broad range of biological and pharmacological properties. Consequently, a great deal of attention has been given to the synthesis of these heteroarenes and reviews covering some synthetic aspects of this topic have been published in recent years. However, none of these reviews provides a comprehensive overview of the catalytic methods developed in the literature for the preparation of this important class of heteroarenes. This article aims to provide an updated critical picture of the catalytic processes reported in the literature up to the end of 2017 for the synthesis of 1,2,4,5‐tetrasubstituted‐1H‐imidazoles illustrating these protocols and their characteristic features such as scope, efficiency, versatility, and limitations. The review also summarizes the mechanisms proposed for many of the reported processes. 1. Introduction 2. Syntheses via one‐pot four component condensation reactions 2.1. One‐pot four‐component syntheses carried out using homogeneous catalysts 2.2. One‐pot four‐component syntheses carried out using heterogeneous catalysts 2.3. One‐pot four‐component syntheses carried out using ionic liquids as catalysts or dual catalysts‐solvents. 3. One‐pot three‐component syntheses 4. Syntheses via [3+2] or [2+2+1] annulation reactions 5. Syntheses via cyclization of propargyl guanidines 6. Syntheses via protocols involving a thiazolium‐catalyzed reaction of aldehydes with α‐amidosulfones 7. Syntheses via oxidative/dehydrogenative coupling reactions 8. Syntheses via Pd‐catalyzed direct arylation of imidazole substrates 9. Syntheses via Pd‐catalyzed cross‐coupling reactions involving the use of stoichiometric amounts of organometallic compounds 10. Syntheses via Pd/Cu‐catalyzed Sonogashira‐type reactions 11. Syntheses via the aza‐Wittig reaction 12. Syntheses from 2H‐aziridines 13. Other synthetic methods 14. Conclusion