Hexafluoroacetone as a protecting and activating reagent. Regioselective esterification of aspartic, malic, and thiomalic acid

Hexafluoroacetone reacts with α-functionalized α,β- dicarboxy acids like aspartic, malic, and thiomalic acid to give exclusively five-membered lactones. The β-carboxylic groups remain unaffected and can be derivatized separately. They can be linked i.a. to orthogonal protecting groups or multivalent alcohols like pentaerythritol to give synthetically valuable building blocks.