Dearomatization of naphthalene: Novel stereoselective cyclization reactions promoted by osmium(II)

A series of Michael accepters has been combined with the Os(II) eta(2)-naph thalene complex (1) to form stable 1H-naphthalenium species. Under acidic c onditions, these complexes undergo ring closure at C2 to form the phenanthr enone core. In contrast, the corresponding l-methylnaphthalene complex (15) upon addition of MVK at C8 undergoes ring closure at C5 to form a bridged tricyclic complex (18). Michael addition of MVK to the naphthalene complex (1) followed by deprotonation, an inter-ring linkage isomerization, and rin g closure forms a 9-methylphenalene complex (21). In all cases, the organic cyclization products may be decomplexed by heating with silver triflate an d isolated in moderate yield.