Benzocyclobutenes. Part 7. Synthesis and X-ray crystal structure of cyclobuta[I]phenanthrene-1,2-dione and the synthesis of hexabenzo[a,c,g,i,m,o]triphenylene

Abstract

[2 + 2] Photocycloaddition of tetrachloroethene to phenanthrene gives 1,1,2,2-tetrachloro-1,2,2a,10b-tetrahydrocylobuta[I] phenanthrene. Treatment of this compound with N-bromosuccinimide gives the corresponding tetrachlorodihydrocyclobutaphenanthrene which can be hydrolysed to cyclobuta[I]phenanthrene-1,2-dione. The ¹H and ¹³C n.m.r. spectra and X-ray molecular structure of the dione have been determined. Flash-vacuum pyrolysis of the dione gives a low yield of hexabenzo[a,c,g,i,m,o]triphenylene.