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
The synthesis of ionic‐liquid‐supported diaryliodonium salts is described. The synthesis is simple and practical, and the ionic liquid products require no chromatographic purification. The ionic‐liquid‐supported diaryliodonium salts are quite stable, and they did not show any sign of decomposition or loss of reactivity, even after being stored for one month at 5 °C. The reactivity of these salts was explored in the phenylation of substituted phenols and carboxylic acids, and the corresponding diaryl ethers and aryl esters, respectively, were synthesized in good to excellent yields and with high purities.
A direct one-pot synthesis of chromeno-annulated imidazo[1,2- a]pyridines is achieved by the reaction of 2-amino-1-(2-ethoxy-2-oxoethyl)pyridinium salts with 2-bromoarylaldehydes using Pd(TFA) as a catalyst and Cu(OAc) as an oxidant. The overall strategy involves tandem base-mediated amidation and Knoevenagel condensation, followed by palladium-catalyzed Wacker type oxidation and intramolecular C-O coupling reaction. The method is simple, tolerates different functional groups, and gives moderate to good yields of chromeno[2',3':4,5]imidazo[1,2- a]pyridin-12-one derivatives. The developed tandem reaction was also successfully applied for the synthesis of pyrano-fused imidazo[1,2- a]pyridines by using 3-bromo-3-arylacrylaldehydes.
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