A novelregioselectivereaction of styrene with the prepared magnesium organoselenolates from magnesium, alkyl or aryl bromides, and selenium has been developed in one pot. The reaction catalyzed by CuI and l-proline proceeded in THF, water, and toluene. The scope and limitations of this reaction have been examined. The reaction afforded unsymmetrical selenides containing 12 new compounds in good to