Oxidation of Hydroquinone Silyl Esters to Quinones

Article abstract of DOI:10.1021/ja00535a030

The electrochemical oxidation of trialkylsiloxybenzene derivatives was investigated using platinum and graphite anodes in either acetonitrile or methylene chloride solvent.Preparative oxidation of the bis(trimethylsilyl) ethers of hydroquinone, chlorohydroquinone, 2,5-di-tert-butylhydroquinone, and 9,10-dihydroxyanthracene gave the corresponding quinones in 80-90percent yield.Oxidation of 1,4-bis(trimethylsiloxy)-2-methoxybenzene in acetonitrile gave 3,6-dihydroxy-2,7-dimethoxydibenzofuran in 65percent yield.Oxidation of 1-methoxy-4-(trimethylsiloxy)benzene in methanolic acetonitrile produced 1,1-dimethoxy-2,5-cyclohexadien-4-one in 99percent yield.The cyclic voltammograms of the trimethylsilyl, triethylsilyl, and tert-butyldimethylsilyl ethers of 2,5-di-tert-butylhydroquinone were recorded using acetonitrile and methylene chloride solvents at 25 and -60 deg C.These compounds were found to react by initial one-electron oxidation to generate a cation radical which decomposes by silicon-oxygen bond cleavage to eventually form quinone.The relative rates for decomposition of the trimethylsilyl, triethylsilyl, and tert-butyldimethylsilyl ether cation radicals at -60 deg C were 10:5:1. tert-Butyldimethylsilyl chloride and tert-butyldimethylsilyl triflate were found to be stable toward cathodic reduction in dry methylene chloride and acetonitrile at potentials as negative as -2.1 vs.Ag/0.1 M AgNO3.Cyclic voltammetry indicated that reduction of 2,5-di-tert-butylbenzoquinone, anthraquinone, and naphthoquinone in the presence of tert-butyldimethylsilyl chloride resulted in reductive silylation.