5-Butylthevinone: stereochemistry of the Diels-Alder reaction of 5-butylthebaine with 3-buten-2-one

In this paper, we report on the X-ray analysis of 5-butylthevinone (7alpha-acetyl-4,5alpha-epoxy-3,6-dimethoxy-5beta-butyl-17-methyl-6alpha,14alpha-ethenoisomorphinan), C27H35NO4. This compound is the sole product of a Diels-Alder reaction of 5-butylthebaine with 3-buten-2-one, through attack of the dienophile on the beta-face of the diene, even though it has been suggested that the introduction of 5beta-substituents tends to hinder attack from the beta-face, and leads to the production of exo-etheno adducts through attack from the alpha-face.