On the reactions of superoxide with keto enols, aci-reductones and ascorbic acid derivatives.
The superoxide-mediated base catalyzed autoxidation of alpha-oxo enols is initiated by the deprotonation of the labile hydroxyl group. Thus, the reaction of O2-. (generated from KO2/crown ether in aprotic media) with 3-hydroxycoumarin (1), followed by a CH3I-workup, generates products 2-4 via a deprotonation-oxidation sequence complicated by a competing saponification of the lactone linkage. The related coumarin reductone (alpha-oxo enediol) 8 is rapidly oxidized by O2-., HO- and t-butoxide to the corresponding triketone, which in turn undergoes further oxidation and rearrangement ultimately yielding (upon methyl iodide workup) products 9-14. When the O2-. mediated oxidation is carried out under argon in completely degassed solutions, large amounts (greater than 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 O2-. with the reductone ascorbic acid.
Frimer
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Ethel and David Resnick Chair in Active Oxygen Chemistry, Department of Chemistry, Bar-Ilan University, Ramat Gan, Israel.
Marks
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Gilinsky-Sharon
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D000438:Alcohols / Q000378:metabolism*; D001205:Ascorbic Acid / Q000378:metabolism*; D003374:Coumarins / Q000378:metabolism; D043844:Crown Ethers; D004988:Ethers, Cyclic / Q000378:metabolism; D005609:Free Radicals; D007659:Ketones / Q000378:metabolism*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D013481:Superoxides / Q000378:metabolism*
D000438:Alcohols; D003374:Coumarins; D043844:Crown Ethers; D004988:Ethers, Cyclic; D005609:Free Radicals; D007659:Ketones; D013481:Superoxides; C015762:18-crown-6; D001205:Ascorbic Acid