By reaction with ammonium persulfate the easily available diselenide derived from (1R)-(+)-camphor was converted into the camphorselenenyl sulfate. This chiral electrophilic selenium reagent reacted at room temperature with alkenes in the presence of methanol to afford selenomethoxylated adducts in good yields and with moderate to good facial selectivity. The two diastereomeric addition products could be separated in most cases. (C) 1998 Elsevier Science Ltd. All rights reserved.