[C:1]1(=[O:20])[N:5]([C@@H:6]([CH2:10][CH2:11][CH2:12][CH2:13][OH:14])[C:7]([OH:9])=[O:8])[C:4](=[O:15])[C:3]2=[CH:16][CH:17]=[CH:18][CH:19]=[C:2]12.[C:21](=O)([O-])[O-].[Cs+].[Cs+].CI>CN(C)C=O.C(OCC)(=O)C>[C:4]1(=[O:15])[N:5]([C@@H:6]([CH2:10][CH2:11][CH2:12][CH2:13][OH:14])[C:7]([O:9][CH3:21])=[O:8])[C:1](=[O:20])[C:2]2=[CH:19][CH:18]=[CH:17][CH:16]=[C:3]12
A slurry of (S)-2-phthalimido-6-hydroxyhexanoic acid (3.752 g., 13.5 mmol.) and cesium carbonate (2.178 g., 6.7 mmol.) in dimethylformamide (44 ml.) was treated with methyl iodide (3.0 ml., 6.84 g., 48.2 mmol.). After stirring at room temperature for 2 hours, the mixture was diluted with ethyl acetate and washed successively with water containing a small amount of sodium bisulfite, water, 50% saturated sodium bicarbonate, and brine, then dried (sodium sulfate), filtered and stripped to give the title product as a colorless oil (3.825 g.). The oil was homogeneous by TLC (1:1-acetone:hexanes) Rf =0.37.
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