Sterically Crowded Heterocycles. I. Molecular Structure of 3-Chain Substituted 2-Phenylimidazo[1,2-a]pyridinium Salts

Abstract

2-Phenyl-3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridine (I) was converted to corresponding 1-alkyl-2-phenyl-3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridinium salts III - VI and 2-phenyl- 3-[(Z)-1,3-diphenyl-3-oxopropenyl]imidazo[1,2-a]pyridinium perchlorate (VII). The protonation site is discussed in terms of calculated molecular energies of alternative cations. The X-ray structure analyses of enone I and its quaternary periodide III are reported and compared with the PM3 molecular optimizations. 1H NMR and 13C NMR spectra reveal well changes of molecular structures caused by the transformation of the base I into salts III - VII.