room temperature, 30 min, followed by hydroxyselenati~ nl~ with PhSeC1/THF/Et3N/Hz0, room temperature, 1 h, yielded the a-selenoaldehyde 15* in 90% yield. Several trials to obtain the enal system (cf. 16 and 17, Scheme 111) under usual conditions (30% H202, NaI04, etc.) were not successful. However, oxidative removal of the selenide with O3 (CH2C12,-78" C), followed by trapping of the resultant ben-