Hydroquinones, silyl-protected

PCC can used for the oxidation of silyl-protected hydroquinones to quinones, except where there are electron-withdrawing substituents on the aromatic ring. Interestingly, there was no evidence for cleavage of the silicon-oxygen bond as the first step, which might be expected under the acidic conditions of a PCC oxidation. 

Polar functional groups such as alcohols or phenols 11 or trimethylsilanol 4 are transformed by monofunctional silylating reagents Me3SiX 12 into their hpophilic and often volatile trimethylsilyl ethers 13 whereas water is converted into persilyl-ated water (=Me3SiOSiMe3, hexamethyldisiloxane, HMDSO, 7, b.p. 100 °C). The persilylation of phenols and, in particular, catechol (or hydroquinone) systems (Scheme 2.1) protects them efficiently against air oxidation even at temperatures of up to 180 °C. (cf, e.g., the silylation-amination of purine nucleosides with dopamine hydrochloride in Section 4.2.4)... 

Trimethylsilylphenyltelluride could also be used to efficiently bis-silylate quinones to the corresponding bis-protected hydroquinones (Scheme 62) [ 173]. The reaction required two equivalents of the silyltelluride and diphenylditel-luride was also isolated. The proposed mechanism is slightly different from above, featuring an initial single electron-transfer to form the quinone radical-anion, which was presumably silylated to form phenoxyl radical 192. Subsequent reaction with trimethylsilylphenyltelluride delivered 193 and diphenylditelluride. 

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