Boronic neighboring group effect

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 ... 

Borontrichloride and boron tribromide have been studied further as dealkylating agents with regard for specificity and neighboring group effects. 

As exemplified with the synthesis of 105 (Scheme 1.2), the latter compounds are obtained via the displacement a-chloroalkylboronates with the hexamethyldisilazide anion. This example also emphasizes the powerful neighboring group effect of boron, which allows selectivity in the addition of Cl2CHLi in the presence of a primary alkyl bromide [323]. Other applications of (a-haloalkyl)boronates in stereoselective synthesis are detailed in Chapter 8. 

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