Benzilic Acid Rearrangement

1,2-Diketones undergo a rearrangement in the presence of strong base to yield α-hydroxycarboxylic acids. The best yields are obtained when the subject diketones do not have enolizable protons.
The reaction of a cyclic diketone leads to an interesting ring contraction:

Ketoaldehydes do not react in the same manner, where a hydride shift is preferred (see Cannizzaro Reaction)

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Mechanism of Benzilic Acid Rearrangement