Oxocarbons and related compounds. Part 28. Polycycle-fused dihydrobenzocyclobutenediones and benzocyclobutenediones. Synthesis of cyclobuta[c]- and cyclobuta[a]-phenanthrene-1,2-diones and cyclobuta[a]triphenylene-11,12-dione

The Diels-Alder reaction of semisquaric chloride 5 with 1-(alk-1-enyl)napht halenes, 2-(alk-1-enyl)naphthalenes and 9-vinylphenanthrene is used to prep are dihydrocyclobuta[c]phenanthrene-1,2-diones 8a-c, dihydrocyclobuta[a]phe nanthrene-1,2-diones 12a-c, and dihydrocyclobuta[a]triphenylene-11,12-dione 18, respectively. Treatment of the dihydrocyclobutaarenediones with bromin e effects aromatization and opens up a route for the synthesis of cyclobuta [c]phenanthrene-1,2-diones 9a-c, cyclobuta[a]phenanthrene-1,2-diones 13a-c and cyclobuta[a]triphenylene-1 1,12-dione 19. The range of Diels-Alder reac tions with semisquaric chloride 5 is extended to the use of 4-(prop-1-enyl) -1,2-dihydronaphthalene 14. Tetrahydrocyclobuta[a]phenanthrene-1,2-dione 15 is obtained in 69% yield, which can be oxidized, stepwise or at once, to g ive cyclobuta[a]phenanthrene-1,2-dione 13b in good yields.