Dearomatization of naphthalene: novel stereoselective cyclization reactions promoted by Osmium(II)

A series of Michael acceptors has been combined with the Os(II) eta(2)-naphthalene complex (1) to form stable 1H-naphthalenium species. Under acidic conditions, these complexes undergo ring closure at C2 to form the phenanthrenone core. In contrast, the corresponding 1-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 ring closure forms a 9-methylphenalene complex (21). In all cases, the organic cyclization products may be decomplexed by heating with silver triflate and isolated in moderate yield.