Annulenes 10 annulene, isomeric structures

The field of metallabenzenes is under active investigation, with numerous reports being published each year. A brief listing of references that have not been cited above is given according to the metal ruthenabenzenes [300-302], platina-benzenes [303,304], iridabenzenes [305], osmabenzenes [306], Haley and coworkers observed that in some instances the formation of metallabenzenes from vinylcyclo-propenes competes with valence-isomeric benzvalenic structures [307, 308] (for a systematic survey of valence isomers of annulenes an earlier three-volume book may be consulted [309]). 

Tetraacetylenes such as 115 and 116 contain the 1,5-hexadiyne group as a bridging element. Since the base-catalyzed isomerization of this unit to hexa-l,3-dien-5-yne (6) constitutes the basic reaction of Sondheimer s annulene chemistry [75], it appeared attractive to attempt to apply this classic reaction of planar aromatic chemistry to a layered precursor and create three-dimensional relatives of Sondheimer s dehydroannulenes. Indeed, both 115 and 116 could be isomerized to their fully conjugated isomers 129 and 130, respectively, by treatment with potassium tert-butoxide in tert-butanol, the original Sondheimer conditions (Scheme 28). From the X-ray structure obtained for 130, it was concluded that both hydro-... 

They have reached similar conclusions concerning the two isomeric [14]annulenes. Isomer A (p. 146) definitely has the structure 9 as previously assigned, but Isomer B probably has the configuration 71. 

Other compounds which might be mentioned, because they illustrate applications of the method to distinctly non-planar systems, are the bridged annulenes bicyclo[4,4,l] undecapentaene f 12] and the isomeric[5,3,l] compound [13]. The x-ray structure is known for [12] and the calculated values are in quite good... 

Bicyclic—monocyclic valence isomerization of a radical dianion in the bicyclo[3 1.0]hexanesemidione system has been demonstrated. Symmetrical 1,4-semldiones formally derived from cycloheptatriene and cyclobctatetraene perfer to exist in the bicyclic (4.1.0 and 4.2.0) structures. Bicyclic—monocyclic valence isomerization in the bicyclo[4.1.0]hept-3-ene-2,5-dione system occurs more readily for the dianion than for the radical anion. Several radical anions derived from the (CH)6 io annulenes are reported. In the case of the 1,2-oxygenated derivatives of (CH)io the dianions or radical anions are stable, but the diones undergo valence isomerization and under oxida-time conditions are converted to 4-hydroxynaphthalene-1,2-semiquinone. Enediol dianions in the bicyclo [2.2 l]hepta-2,5-dione and l-carbQalkoxybicyclo[3 2.1] octa-2,6-diene systems have been observed to undergo... 

---