The reaction of methyl ketones with catalytic amounts of diphenyl diselenide and an excess of ammonium peroxydisulfate in methanol proceeds smoothly to afford a-keto acetals in good yield. In some cases reaction yields were increased by using stoichiometric amounts of PhSeSePh. It is suggested that the oxidation of PhSeSePh by (NHJ2S20s produces a very electrophilic phenylselenenylating agent that effects the methoxyselenenylation of the ...