Norbomane rearrangement

Non-Kolbe reactions are often favoured by skeletal reaiTangements which generate a more stable carbonium ion. Reaction of the cyclic ketal 22 is driven by formation of a carbonium ion stabilised by the oxygen substituent [114]. Reactions of nor-bomanecarboxylic acids are driven by the norbomane carbonium ion rearrangement [115, 116], Oxidation of adamant-1-ylacetic acid in methanol affords 1-methoxyhomoadamantane via a skeletal rearrangement [117],... 

For the norbomyl cation (22), on the other hand, the average 13C chemical shift for C—1,2 was found at 126.1 ppm (at -150°C where all other rearrangements except for the degenerate alkyl shift are frozen out )55)- Thus, C-1,2 absorb by ca. 80 ppm further upfield that the corresponding carbons of the equilibrating ion (25). A similar discrepancy (85 ppm) is estimated on the basis of isopropyl cation and C—1 of norbomane as a model. Some doubt, however, remains whether these acyclic ions are good approximations of the hypothetical 2-norbornyl cation. 

The PMR spectra give no possibility to chose between the nonclassical ion 5 and the rapid equilibrium of a pair of enantiomeric classical ions 6. The ion structure was therefore studied by Raman laser spectra, because the rates of vibrational transitions are far higher than those of Wagner-Meerwein rearrangements. The spectrum of the norbomyl cation proved to be very similar to that of nortricyclejie and quite different from that of norbomane. For rapidly equilibrated classical ions 6, the RS spectrum would be similar to that of norbornyl derivatives. Besides, the rapid equilibration, according to Olah, would lead to the doublet splitting of the bands of some skeletal deformational vibrations which is not observed. 

The olefins (876a) and (876b) afford mixtures of dihalides and acetoxyhalides on reaction with PdClj-CuCl in acetic acid, the 7-substituted norbomane derivatives being formed by typical rearrangements of intermediate norbornyl cations. ... 

The occurrence of carbocationic intermediates in the Hofer-Moest variant of the Kolbe reaction can lead to numerous rearrangement processes. For example, electrolysis of carboxylic acid 68 in methanol results in the oxidative ring opening of the norbomane skeleton[30]. In a similar manner, GroB-type fragmentation of the decaline derivative 70 affords the 10-membered-ring ketone 71 in good yield (Scheme 12) [31]. 

Yellow wormwood Artemisia xantaphora) is reported to contain, among other sesqui- and diterpenes, P-santalene (Corey et al., 1962). This bicyclic compound is presumably derived from farnesyl diphosphate by a somewhat more extensive series of rearrangements including those typical of other norbomane-type skeletons. Presumably, a process such as that shown in Scheme 11.62 is involved. 

The deltacyclane system 1 has a fusion of nortricyclane and norbomane skeletons and is an interesting substrate to study skeletal rearrangements or a-bond partiei-pations in solvolysis processes. 

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