Base-catalyzed oxidation of substituted phenols

Base-catalyzed oxygenation of 2,6-di-t-butylphenols (in which oxidative coupling is hindered) in alkaline alcohol solution yields 2,6-di-t-butyl-4-hydroperoxy-2,5-cyclohexadienones [8-10]  

Nishinaga et al. [11] have observed an interesting regioselectivity in the oxygenation of 2,6- and 2,4-di-t-butylphenols (1 and 2)  

Reversibility of the first step is supported by transformation of the hydroperoxide derived from 4 to 1 (R = t-Bu) upon dissolution in DMF. The analogous reaction for the 2,4-derivative is  

In protic solvents a different regioselectivity is observed. Oxygenation of 1 in t-butanol leads predominantly to the o-peroxyphenolate intermediate 6, which is further converted to epoxy-o-quinol  

The solvent-dependent regioselectivity in the oxygenation of 1 has been interpreted in terms of stability of the peroxy anion Intermediate 4. In polar, nonprotic solvents (DMF, DMSO,HMPT), strong solvation of 

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