Preference of Electron Transfer to Nucleophilic Addition in Reactions of Ketene Silyl Acetals with Quinones and Catalysis of Magnesium Ion

β,β-Dimethyl-substituted ketene silyl acetal (1a) reduces p-chloranil and other activated quinones with electron-withdrawing substituents to produce the carbon–oxygen adduct, the hydrolysis of which yields the corresponding hydroquinone ether. The structure of the hydroquinone ether has been determined by the X-ray crystal analysis. The reactions are significantly slowed down in benzene where the charge-transfer spectra of electron donor–acceptor complexes formed between 1a and the activated quinones are observed. The comparison of the observed rate constant with that predicted for the electron transfer process from 1a to p-chloranil indicates that the addition of 1a to p-chloranil proceeds via the electron transfer from 1a to p-chloranil. Although no reaction takes place between 1a and p-benzoquinone, the electron affinity of which is significantly smaller than that of p-chloranil, the reduction of p-benzoquinone by 1a occurs efficiently in the presence of magnesium ion. The kinetic expression of the Mg2...