Abstract: The synthesis of new optically pure diselenides has been realized in one pot, starting from 2, 2′- diselenobisbenzoic acid and naturally occurring chiral alcohols through a Mitsunobu reaction.They were used to promote electrophilic methoxyselenenylation of styrene, affording moderate to poor diasteroselectivity. The reason of the low stereoselection has been investigated on the basis of 77Se - NMR experiments, evidencing an alternate double coordination with the oxygens of the carboxylic moiety. Some theoretical implications of these interactions in the GPx – like activity of the diselenides will be discussed. Acknowledgements: Financial support from M.I.U.R.-PRIN2007, Consorzio CINMPIS, Bari, University of Perugia, the grant "British- Italian Partnership" from the British Council/CRUI. Financial support from Fondazione Cassa di Risparmio – Perugia, Projects 2011 and 2012.