Conformational study of bridgehead lactams. Preparation and X-ray structural analysis of 1-azabicyclo[3.3.1]nonane-2,6-dione

Abstract

3-(2-Carboxyethyl)-4-piperidone (5), prepared from N-benzyl-4-piperidone and benzyl acrylate (9), was thermally cyclized in the presence of dibutyltin oxide to 1-azabicyclo[3.3.1 ]nonane-2,6-dione (4), which possesses a bridgehead amide nitrogen. The boat–chair conformation of (4) in the solid state has been characterized by X-ray crystal structure analysis and the bridgehead amide shown to be appreciably distorted from planarity, with N(1) displaced by 0.37 Å from the plane of C(2), C(8), and C(9). Crystallographic data are a= 6.214(4), b= 6.845(5), c= 17.850(8)Å, Z= 4, space group P2₁cn. X-Ray intensity measurements were made on a four-circle diffractometer and least-squares adjustment of the atomic parameters converged at R= 0.038 for 1 004 reflections.