Carbon Dioxide → (2R)-2-methyl-3-phenylpropanoic acid

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Reaction Steps

(S)-2-Methyl-3-phenylpropionic acid tert-butylamine salt, reaction time 40 minutes, conversion 100%, ee 96.5% (SFC, 2× Chiralpak AD-H columns, 10% methanol, 3000 psi CO2, 35° C., flow rate 3 ml/minute, retention times R 7.1 minutes, S 7.7 minutes, (E)-phenylcinnamic acid 12 minutes). The free acid was liberated by partitioning between dichloromethane and 2M HCl. The organic layer was dried (Na2SO4), filtered and the solvent was evaporated to give (R)-2-Methyl-3-phenylpropionic acid as a pale yellow solid. [α]D20+98.6, c=2.03, CHCl3. [α]D20+100.6, c=0.54, acetone. [α]D20+103.5 (c=1.00, MeOH). Lit. (M. B. Watson and G. W. Youngson, J. Chem. Soc. C, 1968, 258-261; +140.8, c=2.04, CHCl3). 1H NMR analysis of the (S)-methyl mandelate (E. Tyrell, M. W. H. Tang, G. A. Skinner and J. Fawcett, Tetrahedron, 1996, 52, 9841-9852) confirmed assignment of (S)-configuration.

Provenance & Evidence