Synthesis of novel 5-iodopyrido[1′,2′;2,3]imidazo[5,1-a]isoquinolinium iodides from 2-(2-ethynylphenyl)imidazo[1,2-a]pyridines via iodocyclization

The iodocyclization of alkynes is a facile method for synthesizing essential heterocycles. A simple synthesis for novel 5-iodo-6-substituted pyrido[1′,2′;2,3]imidazo[5,1-a]isoquinolinium iodides via iodocyclization of 2-(2-ethynylphenyl)imidazo[1,2-a]pyridines is presented, which proceeded via 6-endo-digonal cyclization to afford a single product. A variety of desired cyclization products with aryl, vinyl, and alkyl substituents were synthesized under aerobic conditions. X-ray crystal analysis indicated that the cyclization product with the p-tolyl substituent had a significantly planar parent tetracyclic skeleton and the 5-membered ring moiety exhibited resonance character.