Rearrangement neighboring group effects

The reader will no doubt have realized that the y-hetero rearrangement is well-known, being none other than the familiar neighboring group effect. The a-hetero rearrangement is known for all of the elements mentioned but boron, aluminum, and silicon. Perhaps a suitably constituted boron compound would rearrange to a zwitterionic product as follows ... 

A reaction that offers a closer parallel to the neighboring group effect of carbonium ion chemistry is a possible concerted mechanism for the Michael rearrangement ... 

Rearrangements and neighboring group effects intramolecular nudeopldlic attack... 

Neighboring group effects involve the same basic process as rearrangement. Indeed, in many cases there is rearrangement, but it is hidden. What we see on the surface may be this ... 

Further work on chemical structure and reactivity might well include an examination of the possibility of occurrence of an Amadori rearrangement in the case of the glycosyl ureides. In addition, studies of the tautomerism of glycosyl ureides under various conditions of pH and of the neighboring-group effect would be of value in the interpretation of many of the seemingly unorthodox chemical reactions of these compounds. 

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