We developed a novel synthetic methodology for the chemo regio and stereoselective selenomethoxylation of olefins and the selenium mediated cyclofunctionalization of alkenols and alkenoic acids promoted by low-energy blue-led light. The electrophilic species is generated, in situ, starting from diphenyl diselenide according to a self-catalyzed photoredox processes that use atmospheric oxygen as additional oxidant. From a mechanicistic point of view it can be envisioned that the photoactivated homolytic cleavage of Se – Se bond affords a phenylselenenyl radical that can be oxidized by a molecule of oxygen leading the formation of a superoxide anion and the electrophilic selenium species PhSe+ that reacts with C-C double bound affording the formation of a seleniranium ion intermediate able to react regio and stereospecifically with external and internal nucleophiles. Furthermore, the photocatalytically formed PhSe^. radical can react directly with the unsaturated substrates affording a radical selenium containing intermediate that can react with oxygenated nucleophile affording the desired products and a molecule of selenol that is in turn oxidized to diselenide by the atmospheric oxygen. Investigation focused on prove the mechanism and investigate the stereoselectivity also in the presence of preformed chiral centers will be reported and discussed. In our opinion this reaction that can be performed without additives, without external oxidants (apart naturally present oxygen) and without a workup is currently the greener way to perform electrophilic selenenylation reactions in good yield and high selectivity. The use of Santi's reagent (PhSeZnCl) and 1,1'-diselanediylbis(naphthalen-2-ol) as selenium sources will be reported and discussed.