One-step and non-catalytic intramolecular redox reactions of conjugated all E-dienals to non-conjugated Z-enoic acids in subcritical water

Simple treatment of conjugated all E-dienal, (2E,4E)-hexa-2,4-dienal, in subcritical water afforded an intramolecular redox product, non-conjugated Z-enoic acid, (Z)-hex-3-enoic acid, in 42% yield without the usage of a metal catalyst in one-step under the conditions of 250 °C, 10 min, and 0.35 g mL−1 water amount. Similar treatment of the dienal in superheated benzyl alcohol produced corresponding ester, benzyl (Z)-hex-3-enoate, in 34% yield under the conditions of 300 °C, 30 min, and 0.5 g mL−1 benzyl alcohol amount. The obtained (Z)-hex-3-enoic acid was transformed to cis-β-hydroxy-γ-ethyl-γ-lactone in 90% yield by hydrogen peroxide at 60 °C for one day under solvent-free conditions.