The Peterson olefination of aromatic aldehydes with an alpha-silyl selenoacetamide proceeded smoothly with high stereoselectivity to give E-alpha,beta-unsaturated selenoamides in good to high yields. The reaction with aldehydes bearing alkenyl and dienyl groups gave the corresponding selenoamides bearing dienyl and trienyl groups, but the stability of the products depended on the substituents on the aromatic ring. X-ray molecular analysis disclosed that the alpha,beta,gamma,delta-unsaturated selenoamides had a nearly planar structure. In the (77)Se NMR spectra, signals were observed in the region greater than 130 ppm depending on the substituents on the aromatic ring, whereas the (1)J coupling constant between the carbon atom and the selenium atom was almost independent of the substituents. A linear relationship was observed between the chemical shifts in the (77)Se NMR spectra and Hammet sigma parameters, and this correlation was retained even when one or two alkenyl groups were introduced to alpha,beta-unsaturated selenoamides, although it became less sensitive.