Methanol → (alphaS)-4-Chloro-alpha-(1-methylethyl)benzeneacetic acid

Beteiligte Stoffe

Reaktionsschritte

Rhodium-catalyzed hydrogenation. --A catalyst solution was prepared in a glove box (O2 content <1 ppm) by dissolving 0.0482 g (0.1 19 mmol) of [Rh(COD)2 ]BF4 and 0.0858 g (0.1 19 mmol) of (R,S)-BPPFA-EPIP in 20 ml of tetrahydrofuran and stirring at 20° for 15 minutes. Then, 5.0 g (23.74 mmol) of 2-(p-chlorophenyl)-3-methylcrotonic acid, 13 ml of methanol, 33 ml of tetrahydrofuran were placed in a 185 ml autoclave and the catalyst solution prepared above was added. The autoclave was sealed and the hydrogenation was carried out at 20° while stirring and under a constant pressure of 50 bar. The conversion was 100% after 18 hours. The hydrogenation solution was evaporated at 50°/20 mbar and the residue was distilled in a bulb tube oven at 150°/0.2 mbar. There were obtained 4.8 g (96%) of (S)-2-(p-chlorophenyl)-3-methylbutyric acid as a colorless oil which crystallized out at RT; chemical purity 99.9 GC area %; 97.6% ee.

Herkunft & Nachweise