27 メタロセンを活性化剤として用いるC-アリールグリコシド類の合成(口頭発表の部)  [in Japanese] 27 Synthesis of C-Aryl Glycosides Using Metallocene Complex as the Promoter  [in Japanese]

C-Aryl glycosidic bonds are characteristically embedded in several new classes of quinone antibiotics in which the sugars are directly bound to the polyarene chromophores by C-C bond. Unique structures and also the significant bioactivities, e.g., antitumor properties, stimulated growing synthetic interests to these compounds. Recently, we uncovered an efficient glycosidation reaction which utilizes a new activator of glycosyl fluoride, that is, Cp_2MCl_2-AgClO_4 (M=Zr, Hf). We envisioned to apply this new glycosyl activation to the C-aryl glycoside synthesis stated above. The results along these lines is reported herein. (1) Friedel-Crafts Approach to C-Aryl Glycosides: Coupling reaction between glycosyl fluoride and aromatics is efficiently promoted by Cp_2ZrCl_2-AgClO_4 in CH_2Cl_2 at room temperature to give C-aryl glycosides in high yield. Regioselectivity of the reaction of substituted naphthalenes are examined. (2) O→C-Rearrangement Approach to C-Aryl Glycoside: In the presence of Lewis acid, reaction between glycosyl fluoride and phenols gives rise to the O-glycoside as the initial product, which rearranges to its C-congener during gradual warming of the reaction temperature. This two-step reaction, O-glycosidation (Step 1) and O→C-rearrangement (Step 2), proceeds in one pot in the presence of Lewis acid such as BF_3・OEt_2, SnCl_4. Cp_2HfCl_2-AgClO_4 is even more effective in promoting both of the steps. This approach is particularly effective in forming the C-C bond regioselectively at the ortho-position of the phenolic hydroxyl, which is generally complementary to the outcome obtained by the Friedel-Crafts approach. (3) Synthetic Study toward Vineomycin B_2: Based on the tactics stated above, synthetic study toward vineomycin B_2 is undertaken. The reaction between D-olivosyl fluoride 10 and an anthrol derivative 20 cleanly proceeded to afford 21, which is further converted to anthraquinone 22.