Synthesis of benzocyclobutadiene trimers and all-Z-tribenzo[12]annulene. Anew family of concave pi-systems

Nickel-catalyzed oligomerization of trans-1,2-dibromobenzocyclobutene forme d cyclic dimers and trimers. Upon heating, the major anti-cyclic trimer aff orded a cage compound, whereas the minor qm-trimer produced all-Z-tribenzo[ 12]annulene. Dehydrogenation of the anti-trimer with DDQ resulted in the fo rmation of an indenoazulene derivative, and a similar reaction of the syn-t rimer yielded a bowl-shaped system. All-Z-tribenzo[12]annulene was also syn thesized using a stepwise route starting from o-diiodobenzene and o-ethynyl bznzyl alcohol, the overall yield being 22%. All-Z-tribenzo[12]annulene beh aved like pi -prismand and formed chromium(D) tricarbonyl and silver(I) com plexes. (C) 2001 Elsevier Science Ltd. All rights reserved.