Hexa-peri-hexabenzocoronenes by efficient oxidative cyclodehydrogenation:: The role of the oligophenylene precursors

Oligophenylene precursors based on 1,3,5-tris-(2'-biphenyl)ylbenzene (4a) and 1,4-bis-(2'-biphenyl)yl-2,5-diphenylbenzene (5a) were prepared and utilized for efficient hexabenzocoronene (HBC) synthesis by cyclodehydrogenations. Parent HBC 6a was efficiently synthesized from the 1,3,5-tris-(2'-biphenyl)ylbenzene precursor, and novel D-3h symmetrical HBCs were prepared from 1,3,5-tris-(2'-biphenyl)ylbenzenes with various substitution types. For the preparation of a tert-butyl containing HBC 7 with D-2h symmetry, a two-step cyclodehydrogenation was required because of changes in the spin density distribution.