Tetraacetic acid lactone, formation

C. Formation of Triacetic Acid Lactone and Tetraacetic Acid Lactone... 

For more complex metabolites (phenols and tetraacetic acid lactone), further condensation of the triacetyl residue must take place and can only proceed if the priming acetyl residue, with its C-5 oxygen function, is stabilized away from the thioester region of the acyl-enzyme intermediate at this time. Possibly, the presence of NADPH assists in this process, in appropriate enzymes, since the ability to form triacetic acid lactone has been demonstrated by fatty acid and 6-methylsalicylate synthetases when deprived of this nucleotide, but other synthetases have not been tested for this effect. Moreover, the analogous formation of the styrylpyrone bisnoryangonin by flavan-one synthase (Kreuzaler and Hahlbrock, 1975a,b) confirms that the potential for synthesis of stable products with shorter chains does exist. 

Olefins react with manganese(III) acetate to give 7-lactones.824 The mechanism is probably free-radical, involving addition of CH2COOH to the double bond. Lactone formation has also been accomplished by treatment of olefins with lead tetraacetate,825 with a-bromo carboxylic acids in the presence of benzoyl peroxide as catalyst,826 and with dialkyl malonates and iron(III) perchlorate Fe(C104)3-9H20.827 Olefins can also be converted to 7-lactones by indirect routes.828 OS VII, 400. 

Other ways to generate unsaturated acyloxyl radicals have been used. For instance, Moriarty studied the lead tetraacetate oxidation of e carboxylic acid and, after an extensive mechanistic study, he concluded that the y-lactone observed was formed by electrophilic attack on the double bond. " The same explanation can probably be applied to other examples of lactone formation resulting from lead tetraacetate oxidation of ethylenic acids. The formation of a y-lactone has also been reported by anodic oxidation of endo-norbomene-5-carboxylate, possibly by intramolecular addition of the acyloxyl radical but oxidation of the double bond, as proposed for the anodic oxidation of e do-norbornenemethanol, could not be completely discarded. ... 

A novel, high-yielding, and rapid oxidative cyclization of 8-starmyl carboxylic acids has been developed by Yamamoto et al. for the synthesis of 4-hydroxy-8-lactones [81] (Scheme 37). Treatment of p-hydroxy-8-starmyl carboxylic acid 187 with lead tetraacetate facilitated the oxidative cyclization to afford 4-hydroxy-8-lactone 188 in good yield. The presence of the free hydroxyl group in the p-position was essential to coordinate the metal and deliver cyclization and to avoid the formation of an alkene through oxidative elimination. 

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