These enolates provide the following synthetic utility.
What should X be?
- Should confer high reactivity
- Should be cleavable under specific conditions
- Should induce asymmetry. (Malonates are more convenient for systems that do not require asymmetry).
Two of the most widely used are the Evans Oxazolidinone and the Myer's auxiliary.
The Evans oxazolidinone is useful for asymmetric alkylations
The oxazolidinone can be removed in several ways to provide different functionality.
The Myers Auxiliary provides a more reactive enolate that can reactive with electrophiles that do not react with the imide auxiliary.
J. Am. Chem. Soc., 1994, 116, 9361–9362.
The Myers Auxilary can also be cleaved by a variety of conditions.