The Enediolate Chemistry of Free Carboxylic Acids.

The synthetic methodologies for the α-functionalization of free carboxylic acids through the enediolate intermediates are summarized in this review. In general, the enediolates could be generated in situ or transiently from free carboxylic acids with a stoichiometric or catalytic amount of protection reagents, including metal, boron, and silicon reagents. The in situ or transient generated enediolates were subsequently subjected to racemic or asymmetric reactions with various electrophiles, producing the α-functionalized free carboxylic acids in a single step. In addition, the enediolate could undergo an α-oxidation reaction with TEMPO through the radical process.