Facile Diastereoselective Synthesis of Dihydroxyadipic Acid and Dihydroxyadipic Dilactone by Catalytic Reduction of Biosourced 3-Hydroxy-2-Pyrone-6-Carboxylic Acid

3-Hydroxy-2-pyrone-6-carboxylic acid is a versatile chemical easily prepared from aldaric acids, a family of compounds obtained from renewable resources. Herein, an efficient synthesis of dihydroxyadipic acid by catalytic hydrogenation of this pyrone at room temperature and atmospheric pressure is reported. The reaction performed in organic solvents showed high diastereoselectivity, resulting in the possibility to obtain the racemic mixture of dihydroxyadipic acid (R,R) and (S,S) that was further converted to the dilactone 2,5-dioxabicyclo[2.2.2]octane-3,6-dione by a double intramolecular condensation reaction. This compound is a promising comonomer and/or chain-extender in the synthesis of polymers. As an example, a preliminary test of the polymerization reaction of the dilactone in the presence of a diamine is reported.