Syntheses of γ-Oxo Acids or γ-Oxo Esters by Photooxygenation of Furanic Compounds and Reduction Under Ultrasound: Application to the Synthesis of 5-Aminolevulinic Acid Hydrochloride

The photooxygenation of 5-hydroxymethyl-2-furfural (1a) or derivatives 1b-g yields 4-hydroxy-Δ 2-butenolides 2 which are the precursors of butenolides 3 or α,β-unsaturated γ-oxo esters 5. The selective reduction of olides 2 or oxo esters 5 with zinc in acetic acid under sonication leads to γ-oxo acids 4 or γ-oxo esters 6. The photooxygenation of amino derivative 1d, followed by selective reduction of corresponding lactone 2d, gives 5-aminolevulinic acid hydrochloride (7) (ALA) after hydrolysis.