Reactions of complex ligands 85. Chiral quinoid and hydroquinoid [2.2]metacyclophanes via chromium-mediated intramolecular benzannulation

A meta-alkynyl (chromium alkenylcarbene) functionalized benzene 5 is synthe sized in a six-step sequence starting from 3-bromomethyliodobenzene. Upon g entle warming in tetrahydrofuran methoxy[alkynylaryl(alkenyl)carbene comple x 5 undergoes an intramolecular benzannulation to give [2.2]metacyclophane 6 bearing two chiral planes due both to the cyclophane skeleton and the Cr( CO)(3)-coordinated methyl-substituted benzohydroquinone deck. In situ oxida tion of the benzannulation product by cerium(IV) ammonium nitrate directly affords chiral [2.2]metabenzoquinonophane 7. (C) 1999 Elsevier Science S.A. All rights reserved.