Conformations of derivatives of 3,7-diazabicyclo[3.3.1]nonan-9-one. Comparison of 3-ethoxycarbonyl-7-methyl-1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one and 3,7-di(ethoxycarbonyl)-1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one: effect of a nucleophile ⋯ electrophile interaction on molecular geometry

Abstract

X-Ray analyses of 3-ethoxycarbonyl-7-methyl-1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one (4) and 3,7-di(ethoxycarbonyl)-1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one (5) have established that both molecules adopt twin-chair conformations. In compound (5) the urethane N atoms have the expected nearly coplanar arrangement of bonds whereas in compound (4) the urethane N atom has a distinctly pyramidal pattern of bonds; the N–CO₂Et bond in (4) is bent out of the CH₂–N–CH₂ plane towards the NMe group so that the N ⋯ C separation between the NMe and CO₂Et groups is 2.665 Å whereas the corresponding distances in compound (5) are 3.363 and 3.150 Å. The results demonstrate the existence of an attractive nucleophile–electrophile interaction in (4).