Enantioselective Synthesis of Dialkylated α‑Hydroxy Carboxylic Acids through Asymmetric Phase-Transfer Catalysis

In the presence of an L-tert-leucine-derived urea–ammonium salt as phase-transfer catalyst, a highly enantioselective alkylation of 5H-oxazol-4-ones with various benzyl bromides and allylic bromides has been developed to furnish catalytic asymmetric synthesis of biologically important dialkylated α-hydroxy carboxylic acids with a broad scope. This is the first example of an L-amino acid-derived urea–ammonium salt being used as a phase-transfer catalyst with excellent catalytic efficiency.