The superoxide-mediated base catalyzed autoxidation of αoxo enols is initiated by the dcprotonation of the labile hydoxyl group. Thus, the reaction of O-2 (generated from KO 2/ crown ether in aprotic media) with 3-hydroxycoumarin (I). followed by a CH,I-workup, generates products 24 via a deprotonation-oxidation sequence complicated by a competing saponification of the lactone linkage. The related coumarin reductone (αoxo enediol) 8 is rapidly oxidized by O-2, HO- and t-butoxide to the corresponding triketone, which in turn undergoes further oxidation and rearrangenlent ultimately yielding (upon methyl iodide workup) products 9-14. Whcn the O-2 mediated oxidation is carried out under argon in completely degassed solutions, large amounts (≥ 20% of monodeprotonation product (detected as 9) accumulate. These results are discussed in light of the differing mechanisms proposed by Sawyer and Afanas'ev for the interaction of O-2 with the reductone ascorbic acid.
- Ascorbic acid derivatives
- Keto enols. reductones
- Superoxide mediated oxidation