Palladium-Catalyzed Domino Coupling Reactions of Aryl Halides with Norbornene Derivatives - A Simple Route to Polycyclic Aromatic Compounds

Abstract

Under palladium-catalysis, norbornene 1, dicyclopentadiene 10, norbornenol 13, and norbornenone 15 react with unsubstituted as well as substituted bromo- and iodobenzenes to give 1 : 3 coupling products with 4-aryl-9,10-dihydrophenanthrene units with up to 70% isolated yields. The structures of two such products 4a and 4e were proved by X-ray crystal structure analysis. 2-Bromothiophene 17 reacts with 1 and 10 to yield a mixture of 2 : 1 and 3 : 1 coupling products, while 3-iodopyridine 22a, 3-iodo-6-methylpyridine 22b and 4-iodopyridine 25 give only 2 : 1 coupling products with 5,6-dihydro-3,8-phenanthroline and 5,6-dihydro-2,9-phenanthroline units, respectively. Some new mechanistic insights into this interesting four-component domino coupling reaction are presented. The products can easily be transformed by photocyclization/dehydrogenation and/or flash vacuum pyrolysis to a variety of cyclopentadiene-anellated polycyclic aromatic compounds in very high yields. The reported sequence also presents the easiest access to benzo[e]pyrene.