28 コバルトポルフィリン触媒を用いる還元的酸素付加反応の天然物合成への応用(口頭発表の部)

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Cobalt(II) porphyrin-catalyzed reduction-oxygenation of α,β,γ,δ-unstaturated carbonyl compounds with molecular oxygen (1 atm) and triethylsilane in CH_2Cl_2-i-PrOH at room temperature proceeded smoothly and regioselectively to afford γ-hydroperoxy-α,β-unsaturated carbonyl compounds in good yields (Scheme 1 and Table 1). The obtained hydroperoxides were converted in one pot into γ-oxo-α,β-unsaturated carbonyl compounds by treating with acetic anhydride and 4-(N,N-dimethylamino)pyridine (DMAP), and into γ-hydroxy-α,β-unsaturated carbonyl compounds by reducing with trimethyl phosphite, respectively. By the application of this reductive oxygenation, we attempted total syntheses of natural products such as antibiotic macrolide (-)-pyrenophorin (1), antioxidant phenol (2) and the related furans (3) isolated from Ginger, 15-HPETE (4), cytotoxic fatty acid (5) isolated from Corn, and furanoid fatty acid (6) (Fig. 1). (-)-Pyrenophorin (1) was synthesized by the Mitsunobu reaction of (2E,7S)-4,4-ethylenedioxy-7-hydroxy-2-octenoic acid (16), which has been prepared via the reductive oxygenation of ethyl (2E,4E,7S)-7-acetoxy-2,4-octadienoate (13) (Scheme 2). Dienone 22 synthesized from vanillin was oxygenated to give γ-hydroxy-α,β-unsaturated ketone 23, which could be converted into 2 and 3. The reductive oxygenation of (2E,4E)-2,4-nonadienal gave (2E)-4-hydroperoxy-2-nonenal (Table1, Entry 3), which can be converted into racemic 4 according to the reported method (Ref. 13). Lipoxygenase-catalyzed oxidation of linoleic acid followed by treatment with CH_2N_2 gave hydroperoxide 26, which was reduced and then acetylated to afford diene 28. The reductive oxygenation of 28 followed by acetylation gave γ-acetoxy-α,β-unsaturated ketone 29, a precursor of 5. On the other hand, dienone 30 obtained from 26 was oxygenated, reduced with (CH_3O)_3P, and then treated with p-TsOH to give 6.
天然有機化合物討論会の論文
1994-09-20

28 コバルトポルフィリン触媒を用いる還元的酸素付加反応の天然物合成への応用(口頭発表の部)

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