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N N cyclocondensations oxidative cyclizations multicomponent reactions rearrangements tandem processes C-H activations/functionalizationsAbstract 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

An efficient one-pot sequential procedure is described for the synthesis of novel azole-fused quinazolines through Pd/Cu co-catalyzed, Ullmann-type coupling followed by cross dehydrogenative coupling of various azoles such as 1H-imidazole, 1H-benzimidazole and 1H-1,2,4-triazole with 2-(2-bromophenyl)-1H-imidazole/benzimidazoles. The developed strategy has offered good yields (52-81%) of diverse N-fused tetra-, penta- and hexa-cyclic frameworks in a single step.

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The vanadium-catalyzed oxidative coupling of substituted 2-arylimidiazo[1,2-a]pyridines to N-methylmorpholine oxide, which acts as both a coupling partner and an oxidant, has been achieved. This reaction was applied to various substituted imidiazo[1,2-a]pyridine and indole substrates, resulting in yields as high as 90%. Mechanistic investigations indicate that the reaction may proceed via a Mannich-type process. This work demonstrates how oxidative aminomethylation can be used as a useful method to introduce tertiary amines into heterocycles, thus providing an alternative method for conventional Mannich-type reactions.