Oxygen → (2R)-2-(4-fluorophenyl)-3-methylbutanoic acid

Participants

Reaction Steps

In a glove box (argon-atmosphere, O2 -content<1 ppm) a 10 ml measuring flask was charged with 16.9 mg (0.013 mmol) of ((S)-MeOBIPHEP-TS-Na)Ru(OCOF3)2 and filled to the graduation mark with 10 ml of degassed water. The suspension was stirred with a magnetic stirring bar for 15 min at room temperature A clear yellow solution formed. In the glove box a 30 ml stainless steel autoclave fitted with a magnetic stirring bar was charged with 0.5 g (2.57 mmol) of 3-methyl-2-(p-fluorophenyl)crotonic acid, 7.5 ml of degassed water and 0.26 g (2.57 mmol) of degassed triethylamine. To this suspension 2.0 ml of the above catalyst solution was added and the autoclave was then sealed, pressurized with 6 bar of argon and removed from the glove box. The autoclave was connected to a hydrogenation line, which was thoroughly flushed with hydrogen. The argon in the autoclave was replaced by 60 bar of hydrogen and the hydrogenation was carried out by stirring at 20° and 60 bar. After a reaction time of 21 h the autoclave was vented. The light yellow reaction mixture was transferred to a 50 ml separatory funnel, acidified at 20-25° by adding 2.7 ml of 1N aqueous hydrochloric acid and extracted with ether. The combined ether extracts were washed with saturated aqueous sodium chloride solution, dried over sodium sulfate and concentrated to dryness by rotary evaporation. Distillation of the reddish residue at 160° and 0.1 mbar afforded 0.48 g of (R)-2-(4-fluorophenyl)-3-methylbutyric acid as a colorless oil, which solidified on standing at room temperature; ee 84% (determined by GC on a chiral permethylated β-cyclodextrin column); purity>99 GC-area %.

Provenance & Evidence