MORPHINE ALKALOIDS .135. SYNTHESIS OF NEW NEPENTHONE DERIVATIVES

Hydrogenation of nepenthone (3a) leads to a mixture of dihydronepentho ne (3c) and the secondary alcohol (20S)-4b. The enantiomeric secondary alcohol (20R)-4b is prepared from the 7 alpha-formyl-6,14-ethenomorph inan derivative 3b by reaction with phenylmagnesium bromide to afford a mixture of the diastereoisomeric alcohols 4a. Hydrogenation of 4a le ads to (20S)-4b and (20R)-4b, which are separated by fractional crysta llization. The conformations of (20S)-4b and (20R)-4b are determined b y NOE difference experiments.