合成路线1

The Diels-Alder cyclization of butadiene (VII) with 1,4-benzoquinone (VIII) in THF gives the naphthalenetrione (IX), which is acylated with acetic anhydride and TEA to yield the tetralone derivative (X). The Grignard reaction of (X) with vinylmagnesium bromide (XI) and CeCl3, followed by acylation with acetic anhydride, affords the tetraline derivative (XII), which is treated with NaBH4 and oxidized with cerium ammonium nitrate to provide the tetrahydronaphthoquinone (XIII). The cyclization of (XIII) with 4-acetoxy-3,4-dihydro-1H-2-benzopyran-1,3-dione (XIV) by means of NaH in THF gives the intermediate (XV), which rearranges to the tetracyclic dione (XVI). The palladium-catalyzed (PdCl2(MeCN)2) rearrangement of (XVI) in toluene yields the allyl acetate derivative (XVII), which is oxidized with peracetic acid and RuCl3 in water/acetonitrile/dichloromethane to afford the protected intermediate (XVIII). Finally, this compound is deprotected and simultaneously epimerized by a treatment with HCl in refluxing isopropanol/water to provide the desired target intermediate (II).