Practical synthesis of (S)-2-(4-fluorophenyl)-3-methylbutanoic acid, key building block for the calcium antagonist Mibefradil

Article abstract of DOI:10.1016/S0957-4166(97)00498-9

A short, technically feasible route was developed for the synthesis of (S)-2-(4-fluorophenyl)-3-methylbutanoic acid (S)-2 with an overall yield of 80% starting from 4-fluorophenylacetic acid. Asymmetric hydrogenation of the easily accessible unsaturated acid 3 in the presence of ruthenium(II) carboxylato complexes containing chiral atropisomeric diphosphines afforded (S)-2 in up to 94% ee. The ee of (S)-2 was upgraded to 98% by crystallization of its sodium salt. The same protocol was also applied to the synthesis of (S)-2-(4-chlorophenyl)-3-methylbutanoic acid.