1983 年 31 巻 10 号 p. 3411-3417
The chemical transformations of α-santonin (1), a C-6 lactonized eudesmanolide, into C-8 lactonized eudesmanolides, telekin (4) and pinnatifidin (5), are described. Desulfurization of the thio-ketal (8), derived from tetrahydroyomogin (7), with Raney Ni gave the 4-ene (10), which was converted into the α-epoxide (12). Ring-opening of the epoxy ring with LiNEt2 afforded the allyl alcohol (13). Phenylselenenylation of 13 gave the selenide (14), and oxidative elimination then gave telekin (4). Bromination of 3-oxoeudesman-8, 13-olide (18) gave the 2α-bromo-3-ketone (19). Reduction of 19 with NaBH4 gave bromohydrins (20 and 21), which were treated with Zn dust to afford the olefin (22). Treatment of 22 with N-bromosuccinimide afforded the 2-hydroxy-3-bromide (24), which was oxidized to give the 2-oxo-3-bromide (25). Dehydrobromination of 25 afforded the 2-oxo-3-ene (26). Pinnatifidin (5) was synthesized from 26 by phenylselenenylation and deselenoxylation procedures.
