Bridged-bicyclic structures rearrangements

As noted above, the skeletal rearrangements in the 8, 1 reactions and the stereospecificity in the formation of reaction products are essential criteria of the intermediate formation of nonclassical ions. Nevertheless the results obtained can be explained by assuming the C—J bond ionization to proved with a simultaneous shift of the a-bond C —C in the isomer 350 and of the a-bond C —C in the compound 351. The structures 347 and 348 must be transition states of ionization processes. The authors of , however, consider this assumption less probable because the synchronous process in question is a reaction of the 8, 2 type at the bridged carbon atom and for the bridged atoms of rigid bicyclic systems such processes are known to be strongly hindered. The formation of ion 318 with bicyclo[3,2,I]octadiene skeleton consecutively from ion 347 rather than directly from compound 350 with the geometry of bicyclo[2,2,2]octadiene is also in fuller accordance with the principle of so-called least motion " 29)... 

On the other hand, 6-esters of D-glucose and Tyr-terminal peptides rearrange in pyridine-acetic acid (but not in dry methanol, see Seetion n.l.b.vui later) into stable bicyclic D-fiuctosamine structures (26) (Scheme 10). The length and rigidity of the bridging peptide, however, defines its ability to form the Amadori rearrangement products and their tautomeric equilibria in solutions. ... 

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