Hydrogenation of nepenthone (3a) leads to a mixture of dihydronepenthone (3c) and the secondary alcohol (20S)-4b. The enantiomeric secondary alcohol (20R)-4b is prepared from the 7α-formyl-6,14-ethenomorphinan derivative 3b by reaction with phenylmagnesium bromide to afford a mixture of the diastereoisomeric alcohols 4a. Hydrogenation of 4a leads to (20S)-4b and (20R)-4b, which are separated by fractional crystallization. The conformations of (20S)-4b and (20R)-4b are determined by NOE difference experiments.