Oxidative Cleavage of Methyl Ethers Using the HOF･CH₃CN Complex

HOF･CH₃CN complex, made easily by bubbling fluorine diluted with nitrogen through aqueous acetonitrile, proved to be a suitable oxidizer for various methyl ethers. Secondary ethers are oxidized to ketones and even to lactones via Baeyer-Villiger type of oxidation. The reaction is ionic, and the reagent's electrophilic oxygen attacks the relatively electron rich C-H bond a to the ether moiety. It was found that the more sterically hindered is the C-H bond in question, the slower the reaction. In cases where this bond is an electron poor one as in benzoin methyl ether (9), no reaction takes place. When labeled H¹⁸OF-CH₃CN is used on a ¹⁶0 methyl ether, the resulting ketone possesses only the heavier oxygen isotope. Primary methyl ethers are somewhat slower to react, but they too were oxidized in very good yields to acids via the corresponding aldehydes.