Synthesis of Imidazo[1,2-a]pyridines via Near UV Light-InducedCyclization of Azirinylpyridinium Salts

An efficient one-pot synthesis of imidazo[1,2-a]pyridines from 2-bromoazirines and pyridines has beendeveloped. The construction of the bicyclic framework ofimidazo[1,2-a]pyridines occurs in two steps through the formationof (2H-azirin-2-yl)pyridinium bromides followed by dehydrobro-minative UV light-induced cyclization. The method can also beapplied for the synthesis of imidazo[2,1-a]isoquinolines. Unstablein solution, (2H-azirin-2-yl)pyridinium/isoquinolinium bromideswere quantitatively converted to stable tetrafluoroborates, whichcan be cyclized to imidazo[1,2-a]pyridines under UV irradiation in the presence of bromide ions

Automated summary

An efficient one-pot synthesis method for imidazo[1,2-a]pyridines has been developed, which involves the construction of the bicyclic framework of imidazo[1,2-a]pyridines in two steps. The method can also be used for the synthesis of imidazo[2,1-a]isoquinolines. Stable tetrafluoroborates were obtained by converting the unstable (2H-azirin-2-yl)pyridinium/isoquinolinium bromides, which can be cyclized to imidazo[1,2-a]pyridines under UV irradiation in the presence of bromide ions.