In the oxygenation of 4-alkyl-2, 6-di-
tert-butylphenols catalyzed with
t-BuOK in aprotic solvents such as DMF, DMSO, and HMPT, O
2 is incorporated into the para position of the phenols exclusively to give the corresponding epoxy-
p-quinols produced by an intramolecular decomposition of
p-per-oxide anion intermediates. 4-Aryl-2, 6-di-
tert-butylphenols are not susceptible to the oxygenation under these conditions. In the
t-BuOK-catalyzed oxygenation of 2, 4, 6-tri-
tert-butylphenols and 4-aryl-2, 6-di-
tert-butylphenols in
t-BuOH, on the other hand, O
2 is incorporated into the
o-position of these phenols exclusively to give epoxy-
o-quinols. With a large excess of
t-BuOK in DMF the methyl group of
p-cresols is selectively oxygenated to give the corresponding 4-hydroxybenzaldehydes. When 4-alkyl-2, 6-di-
tert-butylphenols are oxygenated in HNEt
2 containing N
aNH
2, the corresponding
p-quinols are obtained in nearly quantitative yield. The
p-quinols are converted quantitatively to hydroquinones with migration of the 4-alkyl group to the adjacent carbon on the ring. The base-catalyzed reaction of acetates of the
p-quinols results in the selective formation of
m-hydroxyphenylacetic acids. It has been newly found that the generation of carbanion adjacent to the carbonyl group in esters of hydroperoxides selectively formed from the
t-butylated phenols extremely weakens the peroxy bond to give unique products even at -70°C. Epoxy-
o-quinols are quantitatively converted to the corresponding cyclopentadienones by base catalysis at an elevated temperature. Cyclopenten-ones are also obtained in good yield from epoxyquinols. A non-radical mechanism for the incorporation of O
2 into the phenolates is argued on the basis of the regioselectivity in the oxygenation and of results obtained in the reaction of phenoxy radicals with O
2-.
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