By using (C 6 H 5 Se) 2–t-BuOOH or (C 6 H 5 Se) 2–(C 6 H 5 SeO) 2 O system, oxoselenenylation reactions of C= C bonds have been examined with allylic and homoallylic alcohol derivatives, and substituted cyclohexenes, and allyl t-butyldimethylsilyl ethers are found to undergo regioselective conversion into β-siloxy α-phenylseleno carbonyl compounds in high yields.