SYNTHESIS OF 2,6-DISUBSTITUTED DIHYDRONAPHTHALENES AND NAPHTHALENES BY ELECTROCYCLIC REACTION OF ORTHO-QUINODIMETHANE - A SYNTHESIS OF (+/-)-NAPROXEN

A survey of the electrocyclic reactions of o-quinodimethanes generated in situ by the thermolysis of dihydrobenzocyclobutenes with a variety of olefinic substituents at C-1 is reported. These reactions provide convenient access to the 2,6-disubstituted dihydronaphthalenes (11) and the naphthalenes (12). Thermolysis of the benzocylobutenes (10) at 180 °C in the presence of manganese dioxide affords in good yields the 2,6-di- and 2,3,6-tri-substituted naphthalenes (12) and (16). The naphthalenes (12b,f,h) thus obtained were easily converted into (±)-naproxen (5).