Page 118 - Catalysts for Fine Chemical Synthesis Vol 1 - Robert & Poignant

104 hydrolysis, oxidation and reduction

hypochlorite is important for the preparation of good quality tert-butyl
hypochlorite. tert-Butyl hypochlorite can be stored in a foil-covered flask
in the freezer for up to 3 weeks without any noticeable change in perform-
ance.
. DHQ 2 PHAL, 71 mg, 0.09 mmol
. 4-Methoxystyrene, 201 mg, 1.5 mmol
. Potassium osmate dihydrate [K 2 OsO 2 (OH) ], 22.5 mg, 0.06 mmol
4
. Saturated aqueous sodium sulfite solution
. Ethyl acetate, petroleum ether (40±60 8C)
. Brine
. Magnesium sulfate

. 50 mL round-bottomed flask with magnetic stirrer bar
. Magnetic stirrer
. Separating funnel, 100 mL
. Rotary evaporator
. Flash chromatography column, 3 cm diameter

Procedure
1. In a 50 mL round-bottomed flask equipped with a magnetic stirrer bar were
placed tert-butyl carbamate (545 mg) and n-propanol (6 mL). A solution of
sodium hydroxide (183 mg) in water (12.2 mL) and tert-butyl hypochlorite
(0.53 mL) were added to the solution. The resulting solution was stirred for 5
minutes and cooled to 0 8C. Then a solution of DHQ 2 PHAL (71 mg) in
n-propanol (6 mL), a solution of 4-methoxystyrene in n-propanol (12.2 mL)
and potassium osmate dihydrate (22.5 mg) were added sequentially to give a
green solution. After 1 hour at 0 8C, the reaction mixture had turned from
green to yellow.
2. The reaction was monitored by TLC (eluent: petroleum ether±ethyl acetate,
1:1). Visualized by ninhydrin dip, the product stained brown-orange, R f
0.43. The 4-methoxystyrene (visualized by UV) has R f 0.72.
3. After completion of the reaction, saturated aqueous sodium sulfite solution
(10 mL) was added and the mixture stirred for 15 minutes. Ethyl acetate
(5 mL) was added and the two phases were separated. The aqueous layer was
extracted with ethyl acetate (3 5 mL). The combined organic extracts were
washed with brine (20 mL), dried over magnesium sulfate, filtered and
concentrated using a rotary evaporator to give the crude product.
4. Purification by flash column chromatography on silica (eluent: petroleum
ether±ethyl acetate, 2:1) gave a crystalline solid (S)-N-(tert-butoxycarbonyl)-
1-(4-methoxyphenyl)-2-hydroxyethylamine (296 mg, 74 %).
The ee (98 %) was determined by HPLC (Chiralcel OD-H column, flow
1 mL/min, eluent: heptane±iso-propanol, 95:5); (S)-enantiomer: R t 11.7 min,
(R)-enantiomer: R t 10.3 min.