B Addition to Generate Metal-Stabilized Cations

As mentioned in previous sections, carbocation intermediates are subject to rearrangement to a more stable ion (sec. 2.7.B.iii). If the cation were stabilized in some manner, rearrangement would be much less likely, as when a heteroatom is attached to the electrophilic carbon. An example is the oxygen stabilized cation (3041 generated by reaction of a ketone with an acid catalyst. The electrons on the heteroatom are donated to the positive center leading to resonance stabilization (this is called back donation). Such a cation is usually 

The use of an alcohol rather than water as the nucleophilic solvent will lead to formation of an ether, and is a simple variation of oxymercuration.243,246 Donaldson s synthesis of the C3-C15 segment of phorboxazole, pyrone 312 was treated with mercuric acetate in methanol.247 Subsequent reduction with sodium cyanoborohydride (sec. 4.5.D) gave a 69% yield of 313 with high selectivity. The intramolecular 

Chapter 2. Acids, Bases, Functional Group Exchanges 

The functional group transform for this reaction type is shown. 

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