Novel process for preparing a 5-hydroxy-3-oxo-hexanoic acid derivative

A process for preparing a compound of formula (1)

• or its tautomer, in which
• R represents hydrogen, saturated-C1-C4-alkyl, or unsaturated-C2-C4-alkyl, and
• X represents halogen, which comprises the following steps:
• 1) (S)-4-halo-3-hydroxybutyronitrile derivative of the following formula (2)
• in which
• X is as defined above, and
• P represents hydrogen or a hydroxy-protecting group, is reacted with an α-haloacetate compound of the following formula (3)
• YCH2CO2R (3)
• in which
• R is as defined above, and
• Y represents Br or I, in the presence of zinc metal activated by an organic acid or its derivative in an organic solvent and
• 2) the product of step 1) is hydrolyzed in the presence of aqueous acid solution.