Page 227 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

employment of catalysts working in tandem 215

Materials and equipment

. Ethyl (Z)-4-acetamido-3-oxo-5-phenyl-4-pentenoate, 275 mg, 1.0 mmol
. [Rh(cod)(S)-BiNAP] CiO ÿ[5] , 9.3 mg, 0.01 mmol
‡
4
. RuBr 2 (S)-BiNAP [6,7] , 8.8 mg, 0.01 mmol
. Distilled triethylamine, 0.14 mL, 1.0 mmol
. Distilled ethanol, 10 mL
. 1 N HCl solution, 20 mL
. Brine, 30 mL
. Ethyl acetate, hexane
. Silica gel 60
. 50 mL Autoclave with glasstube and a magnetic stirrer bar
. Hydrogen gas tank
. Gas connector from tank to autoclave
. Magnetic stirrer
. Oil-bath
. Thermometer
. Syringes
. TLC
. Rotary evaporator

Procedure
1. In a 50 mL autoclave containing a glass tube and magnetic stirrer bar were
placed [Rh(cod)(S)-BiNAP] CiO and RuBr 2 [(S)-BiNAP] as catalysts.
ÿ
‡
4
2. To this mixture were added the substrate 1, triethylamine, and ethanol. The
autoclave was filled with hydrogen (10 atm) after repeated (4±5 times) filling
and purging of hydrogen.
3. The reaction was carried out under 10 atm H 2 at 40 8C for 24 h and under
90 atm at 40 8C for an additional 24 hours.
4. The solvent was removed under reduced pressure.
5. The residue was diluted with ethyl acetate before being washed with 1 N
HCl at 0 8C. The aqueous layer was extracted with ethyl acetate and the
combined organic layer was washed with brine and dried over Na 2 SO 4 .
6. After removal of the solvent, the residue was eluted through a short silica gel
column to remove the catalyst (elution with hexane:ethyl acetate ˆ 1:2). The
eluent was concentrated in vacuo to give the product 2 (99 % yield) and the
diastereoselectivity was determined by HPLC analysis (99 %). The enantios-
1
electivity of the product was determined by H NMR analysis with chiral
shift reagent (‡)-Eu(dppm) in CDCl 3 and by chiral HPLC analysis (Chir-
alcel-OD).