A general procedure for the synthesis of alpha-(phenylseleno)sulfinyl and -sulfonyl alkenes has been described. 1-(Phenylseleno)ethenyl sulfoxides were prepared by the syn-addition of in situ-generated sulfenic acids on to the triple bond of suitably substituted (phenylseleno) acetylenes. 1-(Phenylseleninyl)ethenyl sulfones were obtained by further oxidation of their sulfinyl analogues. The mild conditions of the sulfenic acid/(phenylseleno)alkyne syn-addition and its stereospecificity and regioselectivity allowed us to obtain electron-poor alkenes with a well defined stereochemistry and sensitive substituents at the double bond. Chiral (Z)-1-[(2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl)sulfinyl]-1-(phenylseleno)-1-hexene was also obtained via the enantiopure 2,3,4,6-tetra-O-acetylglucosulfenic acid. The reactivity of alpha-(phenylseleninyl)sulfinyl and -sulfonyl alkenes has been evaluated in nucleophilic additions to the electron-poor double bond, conducted with hard nucleophiles such as piperidine and phenol.