Oxocarbons and related compounds. Part 28.1 Polycycle-fused dihydrobenzocyclobutenediones and benzocyclobutenediones. Synthesis of cyclobuta[c]- and cyclobuta[a]-phenanthrene-1,2-diones and cyclobuta[a]triphenylene-11,12-dione

Abstract

The Diels–Alder reaction of semisquaric chloride 5 with 1-(alk-1-enyl)naphthalenes, 2-(alk-1-enyl)naphthalenes and 9-vinylphenanthrene is used to prepare dihydrocyclobuta[c]phenanthrene-1,2-diones 8a–c, dihydrocyclobuta[a]phenanthrene-1,2-diones 12a–c, and dihydrocyclobuta[a]triphenylene-11,12-dione 18, respectively. Treatment of the dihydrocyclobutaarenediones with bromine 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-11,12-dione 19. The range of Diels–Alder reactions 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 give cyclobuta[a]phenanthrene-1,2-dione 13b in good yields.