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Synlett 1999; 1999(6): 680-691
DOI: 10.1055/s-1999-2700
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π Complexes with Annellated Cyclobutene Rings: Bicyclo[3.2.0]heptadienyl Anion and Benzocyclobutene as Ligands for Transition Metals

Holger Butenschön*
  • *Institut für Organische Chemie, Universität Hannover, Schneiderberg 1 B, D-30167 Hannover, Germany; Fax +49/(0) 5 11/7 62-46 16; E-mail: holger.butenschoen@mbox.oci.uni-hannover.de
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Publication Date:
31 December 1999 (online)

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As was first found on the basis of DSC measurements, bicyclo[3.2.0]heptadienyl cobalt complex 17 undergoes a ring opening - cycloaddition sequence at high temperature with formation of ring expansion products. Benzocyclobutene complexes react in a similar way only in one case. However, deprotonation of benzocyclobutenol complex endo-31 results in a dramatic decrease of the ring opening temperature and allows corresponding [4+2] cycloaddition reactions at low temperature. Benzocyclobutenedione complex 74 shows interesting structural features, its fragmentation in the mass spectrometer leads to a η6 coordinated benzyne chromium cation. Addition of vinylmetal reagents induces a dianionic oxy-Cope rearrangement at -78 °C, the first case of such a reaction at such mild reaction conditions. Products are benzannellated cyclooctenediones and their intramolecular aldol adducts, which are obtained with very high diastereoselectivity.

bicyclo[3.2.0]heptadienyl complexes - benzocyclobutene complexes - cobalt - chromium - dianionic oxy-Cope rearrangement