Oxygen acids, deprotonations, sodium hydride

Oxygen Acids (Alcohol Deprotonation). Sodium hydride may be used as a base in the Williamson ether s)uithesis in neat benzyl chloride, in DMSO, or in THE (eq 2)f Phenols may also be deprotonated and alkylated in THE. ... 

In the example shown the deprotonation of the phosphonate can be achieved under much milder conditions than with the usually employed sodium hydride, which by the way also applies to the standard Horner-Wadsworth-Emmons reagents. Incorporation of the two doubly bound oxygen atoms of the reagent A into sodium chelate B does the trick. Being a cation, B is much more acidic than A and can thus already be deprotonated by an amidine. 

There is another, complementary version of the Peterson reaction that uses base to promote the elimination. The starting materials are the same as for the acid-promoted Peterson reaction. When base (such as sodium hydride or potassium hydride) is added, the hydroxyl group is deprotonated, and the oxyanion attacks the silicon atom intramolecularly. Elimination takes place this time via a syn-periplanar transition state—it has to because the oxygen and the silicon are now bonded together, and it is the strength of this bond that drives the elimination forward. 

The oxazolo[5,4-]pyridine (2) is the exclusive product under these conditions. This product arises from the displacement of the chlorine atom by the amide carbonyl oxygen. A 2.8 molar excess of sodium hydride is required to carry the reaction to completion. The first mole of sodium hydride is consumed with the deprotonation of the more acidic amide protone. 

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