A complete 1D and 2D NMR studies of variously substituted 3-azabicyclo[3.3.1]nonan-9-ones

Variously substituted 3-azabicyclo[3.3.1]nonan-9-ones viz, 2,4-diaryl-3-azabicyclo[3.3.1]nonan-9-ones, 2,4-diaryl-1-methyl-3-azabicyclo[3.3.1]nonan-9-ones and 2,4-diaryl-7-methyl-3-azabicyclo[3.3.1]nonan-9-ones were conveniently synthesized by a modified and an optimized one-pot Mannich condensation of cyclohexanones, benzaldehydes and ammonium acetate in 1:2:1.5 M ratio. All the synthesized bicycles were examined by their physical and spectral (IR, HR-MS, (1)H NMR and (13)C NMR) techniques. In order to establish their unambiguous stereochemical assignments, H,H-COSY, HET-COSY, HMBC, NOESY and dynamic NMR investigations have been carried out for some of the representative compounds. The detailed NMR analysis proved that all the synthesized 3-azabicycles exist in a twin-chair conformation with an equatorial orientation of the substituents, regardless the incorporation of either linear or bulkier groups on the phenyl and/or methyl on the heterocycle or carbocycle. The electronic effects of methylation on the azabicycle as well as the ortho substitution on the phenyl provided some useful insights. (C) 2011 Elsevier B.V. All rights reserved.