Page 178 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

asymmetric reduction using nonmetallic catalysts 165

Materials and equipment

. Anhydrous tetrahydrofuran, 10 mL
. 1-(tert-Butyldimethylsilyloxy)-3-oxo-2-trityloxyiminooctadecane, 1.68 g,
2.5 mmol
. (S)-a,a-Diphenylpyrrolidinemethanol, 63 mg, 0.25 mmol
. Trimethyl borate, 31 mg, 0.3 mmol
. Borane±diethylaniline complex, 815 mg, 5.0 mmol
. 10 M Borane±dimethylsulfide complex, 0.5 mL, 5.0 mmol
. 2 N Hydrochloric acid, 10 mL, 20 mmol
. Sodium hydroxide, 1.4 g, 35 mmol
. Benzoyl chloride, 0.70 g, 5.0 mmol
. Diethyl ether, methanol, methylene chloride, tetrahydrofuran
. Magnesium sulfate
. Silica gel
. 25 mL three-necked flask with a magnetic stirrer bar
. 200 mL round-bottomed flask with a magnetic stirrer bar
. Magnetic stirrer plate
. Oil-bath
. Separating funnel, 100 mL
. Rotary evaporator

Procedure
1. (S)-a,a-Diphenylpyrrolidinemethanol (63 mg) was placed in a 25 mL three-
necked flask equipped with a magnetic stirrer bar, under nitrogen. A solu-
tion of trimethyl borate (31 mg) in dry tetrahydrofuran (5 mL) was added.
The mixture was stirred for 1 hour at room temperature.
2. Borane±diethylaniline complex (815 mg) was added to the resulting mixture.
A solution of 1-(tert-butyldimethylsilyloxy)-3-oxo-2-trityloxyiminooctade-
cane (1.68 g) in dry tetrahydrofuran (5 mL) was added dropwise using a
syringe pump over 1 hour at room temperature.
3. After being stirred for 1 hour at room temperature, 10 M borane±dimethyl-
sulfide complex (0.5 mL) was added. The mixture was heated under reflux for
18 hours. The resulting mixture was cooled to room temperature and cau-
tiously transferred into 2 N hydrochloric acid (10 mL) in a 200 mL round-
bottomed flask equipped with a magnetic stirrer bar using diethyl ether
(10 mL).
4. The same procedure described for the stereoselective reduction of methyl 3-
oxo-2-trityloxyiminostearate gave a white solid N-benzoylsphingamine
(0.96 g, 94 %) as a mixture of diastereomers.
The anti/syn ratio (97:3) and the respective ee (anti 87 %, syn 58 %) were
determined by chiral HPLC.
1
H NMR (270 MHz, CDCl 3 ) for anti isomer d 0.88 (t, J 6.7 Hz, 3H), 1.26
(br, 26H), 1.60 (m, 2H), 2.55 (d, J 6.7 Hz, 1H), 2.63 (br, 1H), 3.82±3.98 (m,