Acetone → (2R)-(4-chlorophenyl)(cyclopropyl)ethanoic acid

Beteiligte Stoffe

Reaktionsschritte

Horse liver esterase (4.6 g horse liver acetone powder, Sigma Chemical Co.) is suspended in water (200 ml) at room temperature and the pH is adjusted to 7.5 with 1.0 M sodium hydroxide. Methyl (2RS)-(4-chlorophenyl)(cyclopropyl)ethanoate (7.0 g, 31.4 mol) is added and stirring is continued at room temperature with the addition of 1.0 M sodium hydroxide as needed to maintain the pH at 7.1-8.0. After 14 ml of base had been consumed, the pH was brought to 3 with 10% hydrochloric acid, ethyl acetate is added and the mixture is filtered through diatomaceous earth. The organic phase is washed with brine, dried over anhydrous sodium sulfate, filtered and concentrated in vacuo. Flash chromatography affords (2R)-(4-chlorophenyl)(cyclopropyl)ethanoic acid (2.5 g, 37.9%) and recovered ester (4.1 g). The ester was resubjected to the hydrolysis conditions with additional horse liver esterase (1.0 g ) for an extended period during which an additional 4.4 ml of 1.0 M sodium hydroxide is consumed. Acidification, workup and purification as described above affords methyl (2S)-(4-chlorophenyl)(cyclopropyl)ethanoate (3.1 g, 36.2%) The enantiomeric excess of (2R)-(4-chlorophenyl)(cyclopropyl)ethanoic acid (as the methyl ester) and (2R)-(4-chlorophenyl)(cyclopropyl)ethanoic acid are determined with the chiral NMR shift reagent Eu(hfc)3 to be >96:4 and >98:2 respectively.

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