Synthesis of Imidazo[1,2-<i>a</i>]pyridines via Near UV Light-Induced Cyclization of Azirinylpyridinium Salts
Ilya P. Filippov, Anastasiya V. Agafonova, Gleb D. Titov, Ilia A. Smetanin, Николай В. Ростовский, Alexander F. Khlebnikov, Михаил С. Новиков
Abstract
An efficient one-pot synthesis of imidazo[1,2-a]pyridines from 2-bromoazirines and pyridines has been developed. The construction of the bicyclic framework of imidazo[1,2-a]pyridines occurs in two steps through the formation of (2H-azirin-2-yl)pyridinium bromides followed by dehydrobrominative UV light-induced cyclization. The method can also be applied for the synthesis of imidazo[2,1-a]isoquinolines. Unstable in solution, (2H-azirin-2-yl)pyridinium/isoquinolinium bromides were quantitatively converted to stable tetrafluoroborates, which can be cyclized to imidazo[1,2-a]pyridines under UV irradiation in the presence of bromide ions.