Formation of enol ethers by alkylation of ketones

cf. Conia, CA 59, 430h. With triethyloxonium fluoroborate or a dialkyl sulfate in aprotic polar solvents, O-alkylation of ketones occurs, and is in fact the major reaction in DMF (dimethylformamide) and DMSO (dimethyl sulfoxide). The % enol ethers obtained at room temp. by adding to an approx. 0.5 M soln. of tert-BuOK in DMSO first 1 equiv. of ketone, and then 1 equiv. of Me2SO4 are as follows: cyclohexanone, 71%; BzMe, 68.5%; Ac2CH2, 71%; and AcCH2CO2Et, 75%. When using 1,2-dimethoxyethane as solvent, cyclohexanone gives 24% of the enol ether. [on SciFinder (R)]