Trifluoroacetyl acetylenes produce [4+2]-adducts solely with thebaine derivatives.
N-Acyl derivatives of thebaine must be used to produce the [4+2]-adducts.
The trifluoroacetyl substituted [4+2]-adducts easily rearrange to benzazocines.
The rearrangement can be prevented by the addition of a nucleophile.
Thebaine itself reacts with trifluoroacetyl acetylenes via a nucleophilic pathway.