反应详情

温度

0 °C

To an ice-cooled solution of 2(R)-(4-methoxybenzenesulfonylamino)-3-methylbutyric acid (30 g, 104.4 mmol), [prepared as described in Example 2, step 1 above], in methylene chloride was added N,N′-diisopropyl-O-tert-butylisourea [can be prepared by the procedure described in Lon J. Mathias, Synthesis, 561-576, (1979)] (75 mL, 3.5 M solution) via additional funnel over 45 min. The reaction mixture was maintained at 0° C. for 2 h, and then allowed to warm to room temperature overnight. Purification by flash chromatography on a silica gel column using (10-20%) ethyl acetate/hexanes as the eluant gave of 2(R)-(4-methoxybenzenesulfonylamino)-3-methylbutyric acid tert-butyl ester (18 g) as a white crystalline solid.

1. customcan be prepared by the procedure
2. temperatureto warm to room temperature overnight
3. customPurification by flash chromatography on a silica gel column