Recent Developments in the Synthesis of Imidazo[1,2-a]pyridines

Advances in the last decade for the synthesis of the imidazo[1,2-a]pyridine scaffold from various substrates employing approaches such as multicomponent reactions, tandem processes, rearrangement reactions, inter- and intramolecular oxidative/reductive cyclizations, and transition-metal-catalyzed C–H activation are summarized in this review. The mechanisms for the selected transformations are also discussed. 1 Introduction 2 From 2-Aminopyridines 2.1 Revisiting Traditional Cyclocondensation 2.1.1 Regioselectivity in Cyclocondensation 2.2 Reactions of Carbonyl Compounds 2.3 Reactions of α,β-Unsaturated Carbonyl Compounds 2.4 Reactions of Nitroolefins 2.5 Reactions of Alkynes 2.6 Multicomponent Reactions 2.6.1 Three-Component Reaction of Aldehyde, 2-Aminopyridine, and Isocyanide 2.6.2 Three-Component Reaction of 2-Aminopyridine, Aldehyde, and Alkyne 2.6.3 Other Multicomponent Procedures 2.7 Reactions of N-Substituted 2-Aminopyridines 2.8 Miscellaneous Reactions 3 From Pyridines 3.1 Multicomponent Reactions 4 From Pyridinium Salts 5 From Imidazoles 5.1 Reactions of Heterocyclic Ketene Aminals 6 Miscellaneous Methods 7 Conclusion