Synthesis and studies of silyl-methyl ketals of quinone

The constant-current anodic oxidation of two types of aryl silyl ethers at platinum electrodes was studied as a synthetic route to quinone bis- and monoketals protected as a silyl-methyl ketal. The first type was monosilyl ethers of hydroquinones, and the second type was silyl ethers of para-methoxy phenols. Yields of 53 to 96 percent were obtained of the desired blocked quinones. The silyl-methyl ketals were shown to undergo smooth decomposition to the corresponding carbonyl compound upon treatment with tetrabutylammonium fluoride in tetrahydrofuran at 10$spcirc$C, indicating that the silyl-methyl ketal may be a useful tool for liberating highly reactive quinone species under mild, non-nucleophilic conditions.;The t-butyldimethylsilyl-methyl benzoquinone monoketal was found to be a useful expedient in the synthesis of para-quinols having acid-sensitive functionality. Addition of eight different organolithium reagents to the quinone monoketal carbonyl afforded generally good yields of the respective quinol ketals as isomer mixtures. Treatment of these para-quinol ketals with tetrabutylammonium fluoride in tetrahydrofuran deblocked the ketals, affording the corresponding quinols. Three quinols that could not be made via a quinone dimethyl monoketal were prepared this way.;A study of the kinetics of the monohydrolysis of six different quinone bisketals demonstrated that the silyl-methyl quinone ketals hydrolyzed nearly 400 times slower than similar dimethyl quinone ketals. To determine the cause of this retardation, the electron donor properties of silyloxy substituents were examined by classical methods and were found to be nearly identical to those of alkoxy substituents. It was concluded based on steric arguments that the hydrolysis retardation is due to poor stereoelectronic overlap of the non-bonded electrons on the silyloxy oxygen with the electron-deficient acetal carbon at the transitions state of the hydrolysis.;The organoaluminum promoted conjugate addition of organometallic reagents to cyclohexenones first studied by Yamamoto was studied as a method of the conjugate introduction of simple organometallic reagents such as Grignard's and organolithiums to quinone monoketals and quinol methyl ethers. Sixteen cases were studied. Also, some further conversions of the initial conjugate adducts were studied.