Treatment of diphenyl diselenide with tributylphosphine in an alkaline medium forms phenylselenolate ion which converts alkyl halides, α,β-unsaturated ketones, and epoxides into alkyl selenides, (phenylseleno)alkenones, and β-(phenylseleno) alkanols, respectively, in high yield. Selenation of 3α-bromocholestane gives 3β-(phenylseleno)cholestane with complete inversion of the configuration.