The SNAr reaction of 1-fluoroxanthone derivatives with alkoxide of 1,1-dimethylallyl alcohol cleanly afforded the corresponding ethers, which have thus far been unavailable. The obtained ethers underwent the Claisen rearrangement at room temperature by treatment with silica gel in toluene. This two-step protocol provides expeditious and high-yield access to xanthones possessing isoprenyl or the related allylic side chain at the C2 position.
2-ジアゾ-3-ケトエステルの化学・立体選択的ロジウム(II)触媒オキソニウム イリド形成-[2,3]-シグマトロピー転位反応を基軸とする天然物 (+)-tanikolide および類縁体の全合成 (Total synthesis of (+)-tanikolide and its analogues based on novel chemoand stereoselective rhodium(II)-catalyzed oxonium ylide formation-[2,3]sigmatropic rearrangement of 2-diazo-3-ketoesters)
An efficient installation of a 3,7-dimethylocta-2,6-dien-1-yl (geranyl or neryl) side chain at the C(1) position of a xanthone core by utilizing an anion-accelerated aromatic oxy-Cope rearrangement is described. Experiments revealed that this uncommon rearrangement takes place in a stereospecific manner through a chair-like transition-state structure. An application to the syntheses of the natural xanthone fuscaxanthone F, possessing a geranyl side chain, and its neryl analogue is also described.
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