Fluoride Tamao-Fleming oxidation

The Fleming oxidation is a two-step process with the second step finding mechanistic similarities in the Tamao oxidation. Principally, treatment of the phenyl(dimethyl)silyl group with HBF4 provides for an electrophilic addition of H+ to the phenyl group to give 5. Attack of the fluoride ion cleaves the carbon-silicon bond, restoring aromaticity in the formation of benzene. 

The silyl groups at the newly formed benzene ring were cleaved by the action of acetyl chloride in anhydrous methanol and tetrabutylammonium fluoride to yield 34 and 35, respectively. A Tamao-Fleming-like oxidation to furnish the respective phenol derivatives did not take place, probably due to the sp -hybridized carbon of the arene moiety. To install the anthraquinone moiety by oxidation of the benzylic positions, it was necessary to reprotect the alcohol functionalities. After tert-butyldimethylsilyl protection of the hydroxyl moieties to afford 36, an iron(III)-catalyzed benzylic oxidation proceeded smoothly with yields up to 70%. Finally, hydrolysis with hydrochloric acid of the protecting groups generated the desired anthracycline derivatives 38 based on a carbohydrate skeleton [21,22] (Scheme 8.8). 

---