2,3-Dihalo- and 2,3,6,7-Tetrahaloanthracenes by Vollhardt Trimerization

We
efficiently synthesized otherwise difficult to obtain 2,3- and
2,3,6,7-halogenated anthracenes with diverse east/west substituents.
Key steps involve the (i) Vollhardt cyclization of bis­(propargyl)­benzenes
with bis­(trimethylsilyl)­acetylene, (ii) halo-desilylation introducing
chlorine, bromine, or iodine substituents, and (iii) dehydrogenation.
Pd catalysis allows selective functionalization at the anthracenes’
east/west positions. A tetrahydropentacene is synthesized and derivatized
via the same strategy, employing tetrapropargylbenzene.