Sinomenine (1) was O-methylated under Mitsunobu conditions to give O-methylsinomenine (2), which was converted into O-methylsinomeninedialdehyde (5) through a procedure of acid hydrolysis, borohydride reduction and thereafter oxidation with NaIO4. Ring-closure of 5 through Adol reaction in the presence of piperidine provided (8S,12S,13R)-6,7-didehydro-3,4-dimethoxy-16-methyl-C-normorphinan-7-
carboxaldehyde (7) with (＋)-C-normorphinan skeleton in a total yield of about 35% from sinomenine. Thereby, compound 8 was prepared by the reduction of 7. And through esterification of 8 with acetic anhy-dride, compound 9 was synthesized. The hydrogenation of 7 with 5% Pd/C as catalyst under 1.01×105 Pa of hydrogen provided compound 10 stereo-directedly. Compounds 11 and 12 were obtained starting from 10. 10, 11 and 12 were determined as of 7S configuration based on the 1H NMR, 13C NMR, 2D-NMR and NO-ESY analysis of compound 11.

Key words: O-methylsinomenine, (＋)-C-normorphinan, sinomenine