Anionic rearrangement carbon stereochemistry

Compounds (5J)—(55)" 102) represent some more substrates which afford rearranged ion pair return products in an apparently stereospecific manner, with inversion at the origin of the 1,2 alkyl shift. Formation of endo-2-norbornyl p-nitroben-zoate from (87) is noteworthy because ion pair return occurs contrary to the natural" exo preference of the norbornyl cation101 The stereochemistry of return may be explained in terms of bridged carbocations. Alternatively the anion may rebond to the same side of the carbon framework from which it departed. Although return to the opposite side was clearly established with allyl cations (Section 4.2.1), reorien-... 

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