A dealkylation reaction of tertiary amines using chloroformate was a useful method for synthesizing morphinan derivatives without 17-substituents; however, the reaction has been applied to only the 14-hydromorphinans. In the course of the investigation of the 17-dealkylation reaction in 14-hydroxymorphinan, the novel cleavage reaction of the C16–N17 bond in the naltrexone derivative was found. A plausible
D-ring would have the loneelectronpair directing in pseudo-equatorial position. These results strongly supported the proposal that the axial orientation of the loneelectronpair on nitrogen would provide sufficient binding abilities to the opioid receptor and that the 15–16 ethylene moiety in the morphine structure would play a role in fixation of the loneelectronpair in the axial direction rather