Triquinacene complexes

Strategies based on known, highly elaborated, but nevertheless readily accesible, starting materials with a "complexity index" as near as possible to the "complexity index" of the target molecule. This strategy has also been applied to non-natural compounds as, for instance, in the synthesis of triquinacene by Woodward [37] and in the syntheses of dodecahedrane by Paquette (Domino Diels-Alder adduct) [38] and Prinzbach ("pagodane") and their associates [39]. 

An example of the inherent complexities in assigning homoaromaticity in neutral hydrocarbons, even when accompanied by thermochemical, molecular mechanical and/or quantum chemical analysis, is shown by the competing studies of the energetics of triquinacene ... 

The scope of the intramolecular Pauson-Khand has been rapidly expanded as both more complex and heteroatom-containing substrates have been employed. Cycloadditions involving a cycloalkene reaction partner afford the direct construction of tricyclic systems in a single step. Triquinacene derivatives are efficiently obtained from 3-(3-butynyl)cyclopentenes [Eq. (55)]. An unusual characteristic of this system is the epimerization that occurs at the pro-pargylic position subsequent to cobalt complexation but prior to cyclization. The steric demands on the reaction are evidently so large that one stereoisomer is unable to cyclize and, instead, isomerizes through a cobalt-stabilized propargylic cation [123]. 

Me, = H 71 %) and (208 R = H, R = Me 21.5 %) was obtained from the iron tricarbonyl complex of methylcyclo-octatetraene. Oxidation of these adducts with ceric (iv) ion gives dihydrotetracyanotriquinacenes in good yield. tcne reacts with the iron-tricarbonyl complex of unsubstituted cyclo-octatetraene to give the 1,3-adduct (208 R = R = H) which is oxidized by cerium (iv) to a dihydrotetracyano-triquinacene. ... 

While some complexes of dihydroacepentalene derivatives have been reported some time ago [178-180], metal complexes of the unstable acepentalene (137), although they were the subject of DFT calculations [181], are still elusive. The acepentalene dianion (138) was obtained as its lithium salt in pure form by treatment of triquinacene (147) with BuLi/KOtBu/TMEDA giving 138 as its impure potassium salt, which was trapped with MegSnCl. The l,7-bis(trimethylstaimyl)-4,7-dihydroacepentalene (148) obtained was then treated with methyllithium, affording pure dilithium acepentalenediide (138-2Li+) (Scheme 10.52) [152]. 

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