6,14-Endoethenotetrahydrooripavine
6,14-Endoethenotetrahydrooripavine is the central nucleus, or backbone, of a class of morphinan opioids known as the Bentley compounds and may be considered their "privileged scaffold". These include but are not limited to etorphine and buprenorphine.
Source: Wikipedia — 6,14-Endoethenotetrahydrooripavine (CC BY-SA 4.0)