1-[2-(Methylsulfanyl)phenyl]prop-2-en-1-one (1) and the seleno congener (2) reacted with acetals 3 and 21 in the presence of BF(3).Et(2)O to give alpha-alkoxyalkyl enones 4, 5 and 22, 23 in good yields. When the reaction mixtures were worked up with a saturated NaHCO(3) solution instead of Et(3)N, onium salts 6 and 7 were obtained together with 4 and 5. Reactions with cyclic acetal 14 gave alpha-(beta-hydroxyethoxy) enones 15 and 16 accompanied by dimeric products 17 and 18.