REACTION OF SUPEROXIDE WITH ACI-REDUCTONES

Three reductones, ihydroxy-4,4-diphenyl-2,5-cyclohexadien-1-one(11), 3 ,4-dihydroxycoumarin (35), and 3,4-dihydroxyspiro[5.5]undecan-3-en-4-o ne (64), were prepared and subsequently reacted with superoxide anion radical(O-2(.-)), generated from KO2 and 18-crown-6 polyether. The rea ctions were carried out in aprotic media and quenched with methyl iodi de which facilitates the trapping of the various oxyanions formed. Whi le a plethora of products were formed in each case roxy-2-methyl-4,4-d iphenyl-5-cyclohexene-1,3-dione (17), dimethyl 4,4-diphenylglutaconate (18), methyl 4,4-diphenyl-3-butenoate (19), phenylcinnamaldehyde (20) , methyl 3-phenylcinnamate (21), and benzophenone (22) from 11; 3-hydr oxy-2-methoxycoumarin (39), 2-carbomethoxy-2-hydroxy-3-coumaranone (40 ), 2-hydroxy-2-methyl-3-coumaranone (41), methyl o-hydroxyphenylglyoxy late (42), methyl salicylate (43), and catechol (44) from 35; and 2,4- dihydroxyspiro[5.5]undeca-1,4-dien-3-one (66), 2-hydroxyspiro[4.5]dec- 1-en-3-one (70), dimethyl 1,1-cyclohexanediacetate (73), and dimethyl alpha-keto-1-[(methoxycarbonyl)methyl]cyclohexane (75) from 64], an ov erall analysis of the product distribution indicates that the basic el ements of the reaction sequence are the same. The first step involves facile deprotonation and the concomitant generation of the reductone m onoanion, a process which lends support to the suggestion of Afanas'ev and co-workers (Afanas'ev, I. B.; Grabovetskii, V. V.; Kuprianova, N. S. J. Chem. Sec. Perkin Trans. 2 1987, 281-285). Oxidation of this mo noanion yields the corresponding triketone. Of the various options ava ilable to this polyketone, superoxide attack at the most electrophilic central carbonyl followed by oxidative cleavage and/or benzylic acid rearrangement are clearly the most prominent. These are followed by a variety of base catalyzed autoxidative processes which are highly depe ndent on the nature of the substrate.