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The first synthesis of Cubane! |
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The cubane system was first synthesized over 35 years ago by Philip Eaton and Tom Cole. It is a highly symmetric cubic cage structure having carbon atoms at the vertices of a cube. The synthesis needs to go through brombromocyclopentadienone dimer I and cubane-1,4,dicarboxylic acid. It is a marvel scheme of economy and simplicity. With only minor modification, this procedure remains to this day the best available method for large-scale synthesis of cubane-1,4,dicarboxylic acid. The detail synthesis is shown in the diagrams on the right hand side. |
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| The stereospecific in situ [4 + 2] (Diels-Alder) cyclodimerization of 4-bromocyclo-pentadienone is the key in this kinetically controlled synthesis. However, it is still a tricky matter and a few years later after this synthesis is published, N.B.Chapman et al in England following up this work and improved this synthesis. | ||||||
Why cubane is stable? |
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| The reason for this, unappreciated at the time
of the early predictions of instability, is that there are no kinetically
viable paths along which cubane can rearrange thermally. On one hand, orbital
symmetry considerations raise the energy of concerted two-bond ring opening
reactions. On the other, there is little to be gained by breaking just one bond as there is concomitantly only a small change in geometry, and the resulting biradical is still very strained. |
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