Cubanecarboxylic acids

Figure 5. Crystal structures of 4-chloro-1 -cubanecarboxylic acid (top left), 4-bromo-1-cubanecarboxylic acid (bottom left), 4-iodo-1-cubanecarboxylic acid (top right) and 4-carbomethoxy-1-cubanecarboxylic acid (bottom right) to show the layer with zig-zag arrangement of synthon VIII.

The repeated occurrence of the otherwise rare catemer VII in the family of cubanecarboxylic acids under study here is quite likely the result of fortification of the catemer by the C-H—O hydrogen bond formed by the acidic cubyl C-H group.1261 This... 

Baker, F.W, Parish, R.C. and Stock, L.M. (1967) Dissociation constants of bicyclo[2.2.2]oct-2-ene-l-carboxylic acids, dibenzobicyclo[2.2.2]octa-2,5-diene-1-carboxylic acids, and cubanecarboxylic acids./. Am. Chem. Soc., 89, 5677-5685. 

Another approach is to study compounds based on derivatives of bicyclo-[2.2.2]octane and cubane. The carbon atoms labeled 1 and 4 are essentially the same distance apart in the two parent compounds ( 0.01 A). There are three different three-bond paths connecting Cl and C4 in bicyclo[2.2.2]-octane, but there are six analogous three-bond paths in cubane. A series of 4-substituted cubanecarboxylic acids (92) and 4-substituted bicyclo[2.2.2]-octane-l-carboxylic acids (93) showed similar effects of a substituent X on the pfCa of each parent compoimd. 

Ring strain of the migrating group is compatible with the Wolff rearrangement and this was, for example, exploited in the homologation of cubanecarboxylic acid 45. ... 

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