C02Me Me OH

Scheme 9 Synthesis of bicyclo- and spiro-dioxanes from ^-ketoesters

The dihydrofurans derived from the overoxidation of the intermediate carbon radicals and the others occurred from the direct oxidation of the alkenes during the electron-transfer mechanism (Scheme 1). In order to depress the side reactions, it was found that a catalytic amount of manganese(III) acetate was enough to produce the cyclic peroxidation reaction. The reaction proceeded only in the presence of manganese(II) acetate in air, although it took a longer reaction time [79-82]. Since the active species in the aerobic oxidation is manganese(III), the presence of various cooxidants, such as cobalt(III) acetate, potassium permanganate, lead(IV) acetate, copper(II) acetate, chromium(VI) trioxide, thallium(III) acetate, ammonium cerium(IV)

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