Studies on the Terpenoids and Related Alicyclic Compounds. XXX. An Application of the Angular Hydroxylation Using Benzeneseleninic Anhydride to the Syntheses of 10β-Hydroxyfuranoeremophilane Derivatives

The syntheses of several 10β-hydroxyfuranoeremophilane derivatives, (±)-10β-hydroxyfuranoeremophilane-3, 6-dione (3), (±)-10β-hydroxyfuranoeremophilan-6-one (4), and (±)-10β-hydroxy-6β-isobutyryloxyfuranoeremophilan-9-one (5), are described. The key step in these syntheses is the angular hydroxylation of 10βH-furanoeremophilane-6, 9-dione (6) using benzeneseleninic anhydride. Reduction of the 10β-hydroxy-6, 9-dione (7) with NaBH4 or ZnNH4OH gave the 9α- or 9β-hydroxy compounds (9a and 10), respectively. The stereochemistries of the diols (9a and 10) were confirmed by the chemical conversion of 9a to the known compound 17. Treatment of 9a and 10 with methanesulfonyl chloride-Et3N afforded the 9β, 10β-epoxide (18). Ring-opening of 18 with NaBH4 gave the 10β-hydroxy compound (21). Deacetalization of 21 with aq. acetic acid afforded (±)-3. Desulfurization of the 3, 3-dithioacetal (24) which was derived from 21 with Raney Ni gave (±)-4. The enone (27a) was treated with isobutyric anhydride followed by catalytic reduction to afford 28b as a major product. Hydroxylation of 28 with benzeneseleninic anhydride in the presence of NaH in chlorobenzene afforded the 10β- and 10α-hydroxy compounds (29a and 29b). Desulfurization of the 3, 3-dithioacetal of 30a which was derived from 29a with Raney Ni gave (±)-5.