Abstract: The ylides Ph3P= CAr'Ar2 la-g (k= C&, pC. &cl, p-C6&F, m-C6&CF3, p-CaOCH3, p- c6&-CH3) were treated with elemental selenium (-80 “C) to give the corresponding selenoketones SeeeCAr'Ar2 2 by Staudinger-chalcogenation. Their reaction with truns, truns- 2, 4-hexadiene proceeds completely stereospecifically to yield the 2, 2-diaryl-3, 6-dihydro- cis-3, 6-dimethyl-2H-selenapyrans 3. In contrast, the reactions of the selenoketones 2 with ...
