Structural study of 3-azabicyclo[3.3.1]nonane derivatives functionalized at 1 and/or 9-positions by molecular mechanics calculations and NMR spectroscopy

Some 3-azabicyclo[3.3.1]nonan-9-ones, 1-3, 1-alkoxycarbonyl derivates, 4, 5 and alpha and beta 3-methyl-3-azabicyclo[3.3.1]nonan-9-ols, 6, 7, have been studied by means of the molecular mechanics (MMX) method and H-1, C-13-NMR spectroscopy. Experimental data fit well with theoretical calculations. It is found that the conformational behaviour of the bicyclic system is governed mainly by steric factors and a flattened chair-chair conformation bearing the N-substituent in the equatorial position (CC-beta) is always preferred. A monoconformational character can be reasonably assumed except for 3-methyl-3-azabicyclo]3.3.1]nonan-9 beta-ol, 7, in non polar solvents where the BC-alpha form should amount to about 15% of the equilibrium mixture. (C) 1997 Elsevier Science Ltd.