The naphthalene complex of pentaammineosmium(II) (1) reacts with four different classes of electrophiles to form 1-naphthalenium species 2-5. These eta(3)-allyl complexes react stereospecifically with a variety of nucleophiles to form cis-1,4-dihydronaphthalene complexes. The entire reaction sequence may be performed outside a glovebox in two steps using conventional techniques.