Conformational study of N-substituted 9-azabicyclo[3.3.1]nonan-3-ones

Abstract

N-Substituted 9-azabicyclo [3.3.1] nonan-3-ones have been studied by 1H- and 13C-NMR spectroscopy. In CDCl 3 solutions, these ketones can be described through an equilibrium between two flattened chair-chair conformers by nitrogen inversion. The piperidone ring is more flattened than the piperidine one and has a slight preference for the form with the N-substituent axial to the piperidone ring. The contribution of the conformers with piperidone or piperidine rings in an ideal boat conformation must be low. The application of the Altona empirical equation supports this hypothesis.