Asymmetric Hydroxylation and Aminohydroxylation

Department of Chemistry, University of York, Heslington, York YO10 5DD, UK 

4mol% K2Os02(OH)4 6mol% (DHQ)2PHAL 2 1 PrOH-water, 0°C, lh 

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°C. Then a solution of DHQ2PHAL (71 mg) in n-propanol (6mL), a solution of 4-methoxystyrene in //-propanol (12.2 mL) and potassium osmate dihydrate (22.5 mg) were added sequentially to give a green solution. After 1 hour at 0 °C, the reaction mixture had turned from green to yellow. 

The reaction was monitored by TLC (eluent petroleum ether-ethyl acetate, 1 1). Visualized by ninhydrin dip, the product stained brown-orange, R 0.43. The 4-methoxystyrene (visualized by UV) has R 0.72. 

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 (3x5 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. 

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