Regioselective N–alkylation of 2– (3,4–dimethoxyphenyl)imidazo[4,5–b] and [4,5–c]pyridine oxide derivatives: Synthesis and structure elucidation by NMR


GÖKER A. H. , Ozden S.

Journal of Molecular Structure, vol.1197, pp.183-195, 2019 (Peer-Reviewed Journal) identifier identifier

  • Publication Type: Article / Article
  • Volume: 1197
  • Publication Date: 2019
  • Doi Number: 10.1016/j.molstruc.2019.07.058
  • Journal Name: Journal of Molecular Structure
  • Journal Indexes: Science Citation Index Expanded, Scopus
  • Page Numbers: pp.183-195
  • Keywords: Imidazo[4,5-b]pyridine-4-oxide, Imidazo[4,5-c]pyridine-5-oxide, Tautomerism, NOESY (nuclear overhauser effect spectroscopy), HMBC (heteronuclear multiple bond correlation), IMIDAZOPYRIDINE, INHIBITORS

Abstract

© 2019 Elsevier B.V.Imidazopyridines can exist in several tautomeric forms such as benzimidazole or purine condensed systems. Regioselectivities were determined for N-alkylations of 2-(3,4-dimethoxyphenyl)- imidazopyridines and their 4 and 5-oxides (2–4, 13, 14) with n-butyl and 4-fluorobenzyl bromides under basic conditions (K2CO3 in DMF). It was observed that N-4 (5–8) and N-5 (15–17) regioisomers were mainly formed. Compounds 7 (N4) and 7a (N1) were separated from the mixtures of regioisomers in a 50: 1 ratio. Their structural assignments were made with the use of two-dimensional 1H-1H NOE (nuclear overhauser effect spectroscopy [NOESY]) enhancements between the N-CH2 and protons on the C-4, 5, 6, and 7 positions of the pyridine moiety. To verify the NOESY data, synthesis of compounds 7a and 7b was achieved by the selective method. Complementary structural information was provided by 2D-HMBC spectra of the compounds.