3, 6-Dimethoxy-4-acetxy-5-[2-(N-methylacetamido) ethyl] phenanthrene (3) and its isomer 3, 6-dimethoxy-4-acetoxy-& [2-(N-methylacetamido) ethyl] phenanthrene (4) have been detected aa manufacturing byproducts at trace levels in illicit heroin. These compounds are novel rearrangement products obtained by the action of acetic anhydride (Ac20) on thebaine (1). The syntheses of 3 and 4 from 1 proceed via the intermediate A6, 7, 9 (14)-N- ...