Synthesis of Unsaturated 1,6-Diketones and 1,6-Diols from Muconic Acid

<i>Cis-,cis</i>-muconic acid (HO₂C-CH═CH-CH═CH-CO₂H) reacts with arenes in Bro̷nsted superacid TfOH, affording the aromatic acylation products, unsaturated <i>E-,E</i>-1,6-diketones [ArOC-CH═CH-CH═CH-COAr]. These diketones are also obtained in Friedel-Crafts acylation of arenes by muconoyl chloride. The reaction in TfOH proceeds through an intermediate formation of muconic acid <i>O,O</i>-diprotonated form [HO(⁺HO═C)-CH═CH-CH═CH-C(═OH)⁺OH], which was investigated experimentally by NMR and theoretically by DFT calculations. Carbonyl reduction of these 1,6-diketones with NaBH₄ results in the formation of the corresponding unsaturated diastereomeric <i>E-,E</i>-1,6-diols [Ar(HO)CH-CH═CH-CH═CH-CH(OH)Ar]. Catalytic hydrogenation of carbon-carbon bonds in 1,6-diketones with Pd or Pt on carbon furnishes the corresponding 1,6-diketones (ArOC-CH₂CH₂CH₂CH₂-COAr). The studied reactions contribute to the development of organic synthesis on the basis of transformations of muconic acid, which is an important compound in industrial chemistry.