2,4-Diaryl-3-azabicyclo[3.3.1]nonan-9-ones with tert-pentyl substituent on the cyclohexane: Complete NMR spectral study

Abstract

A series of 7‑tert-pentyl-2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ones (5-11), as well as three reported analogs (1, 2 and 4) were synthesized, and characterized under identical conditions for comparison. The NMR data were assigned using 1H1H– COSY, NOESY, and HMQC spectral studies. The results suggest that all bicyclic compounds exist predominantly or exclusively in the chair-chair conformation, with an equatorial disposition of phenyl/substituted phenyl groups at C-2/C-4 and alkyl groups at C-7. This was observed regardless of the size or nature of the substituents on the phenyl groups and/or cyclohexane. However, in a few compounds, a minor population of the chair-boat conformer was also observed with an equatorial orientation of phenyl/substituted phenyl groups on the piperidine chair and the tert‑pentyl on the bowsprit orientation of the cyclohexane boat. Lastly, the tert‑pentyl compounds were screened for their antioxidant potency using the DPPH radical scavenging method, and the results were found to be moderate.