Methanol → alpha-Methylhydrocinnamic acid

Participants

Reaction Steps

0.41 g (2.53 mmol) of 2-methylcinnamic acid and 5 ml of degassed methanol are introduced in succession into a Schlenk vessel filled with argon. A catalyst solution consisting of 4.73 mg (0.01265 mmol) of [Rh(norbornadiene)2]BF4, 8.77 mg (0.0133 mmol) of ligand A and 5 ml of degassed methanol is prepared in a second Schlenk vessel filled with argon. This solution and the catalyst solution are then transferred in succession by means of a steel capillary into a 50 ml autoclave filled with argon. The ratio of substrate/catalyst is 200. The autoclave is closed and a pressure of 5 bar is set by means of 4 flushing cycles (pressurization to 10 bar of hydrogen). The autoclave is thermostated at 25° C. and the reaction is started by switching on the stirrer. The reactor is stirred for 19 hours. After opening the autoclave, a reddish reaction solution is isolated. The conversion is quantitative (determined by means of GC and 1H-NMR). Removal of the solvent on a rotary evaporator gives a quantitative yield of 2-methyl-3-phenylpropionic acid having an enantiomeric purity of 29% ee (determined by means of HPLC after conversion into the methyl ester; column: Chiracel OB.).

Provenance & Evidence