Synthesis, structural and conformational study of several acyl derivatives of 9-(2′-hydroxyethyl)-9-azabicyclo[3.3.1]nonan-3α(and β)-ols

Abstract

A series of acyl derivatives of 9-(2′-hydroxyethyl)-9-azabicyclo[3.3.1]nonan-3α (and β)-ols have been synthesized and studied by 1H and 13C NMR spectroscopy. The compounds derived from 9-(2′-hydroxyethyl)-9-azabicyclo[3.3.1]nonan-3α-ol( I) display in CDCl 3 solution the same preferred flattened chair-boat conformation with the acyloxy ring in a slight distorted boat form and the other ring in a chair form, flattened at C7 and puckered at N9. The compounds derived from 9-(2′-hydroxyethyl)-9-azabicyclo[3.3.1]nonan-3β-ol ( VI) can be described, in CDCl 3 solution, as an equilibrium between two flattened chair-chair conformations through nitrogen inversion. A slight predominance of the form with the N-substituent axial with respect to the piperidine ring might be proposed.