Cubane, synthesis

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

Manini, P Amrein, W. Gramlich, V. Diederich, F. Expanded cubane synthesis of a cage compound with a C56 core by acetylenic scaffolding and gas-phase transformations into fullerenes, Angew. Chem. Int. Ed. 2002,4339-4343. 

The choice of the substituent R is critical for the cubane synthesis. For instance, the cyclotetragermane 7a bearing four tert-bu. y groups and four... 

Cyclohexadiene-1,4-dione, 2,5-dibromo- cyclobutane synthon in cubane synthesis, 78... 

When cyclic a-haloketones are submitted to the Favorskii reaction conditions, a ring contraction can be observed. This efllcient procedure has been applied to constrained substrates. The most spectacular example is probably the cubane synthesis achieved in 1964 by Eaton and Cole ... 

The synthesis of cubane has been outlined on p. 78. Cuneiform cuneanes are formed by silver(l)-catalyzed isomerization of cubanes in almost quantitative yield. Rhodium(I), on the other hand, effects isomerization of cubane to a syn-tricyclooctadiene (L. Cassar, 1970). 

With cyclic a-halo ketones, e.g. 2-chloro cyclohexanone 6, the Favorskii rearrangement leads to a ring contraction by one carbon atom. This type of reaction has for example found application as a key step in the synthesis of cubane by Eaton and Cole for the construction of the cubic carbon skeleton ... 

A number of proteins containing [3Fe-4S] centers form cubane-like clustes of the type [M,3Fe-4S] (115-120), which were prepared using this facile [3Fe-4S]/[4Fe-4S] conversion pathway. The [3Fe-4S] core present in D. gigas Fdll was the first precursor used for the synthesis of heterometal cores inside a protein matrix, and the first derivative synthesized was the [Co,3Fe-4S] core (121). Similar synthetic products have also been derived in D. africanus Fdlll (118, 119). 

Only a trace of the corresponding cubane 167 is formed on irradiation of the tricy-clooctadiene 168 in pentane at ambient temperatures using a 125-watt mercury arc lamp. The principal product 169 is the result of rearrangement within a biradical intermediate79. A review of the synthetic approaches to cubane and to its reactions has been published77. The diene 170 photochemically converts on irradiation in pentane solution at 254 nm to yield a photostationary mixture of the cubane 171, the starting material 170 and the isomeric diene 17280. Other additions of this type have been used for synthesis of the propellaprismane 173, essentially a heavily substituted cubane, by the intramolecular (2 + 2)-photocycloaddition of the diene 17481. 

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