C([O:8][C:9](=[O:21])[NH:10][C:11]1C=CC2OCC[O:18][C:13]=2[CH:12]=1)C1C=CC=CC=1.[Li][CH2:23]CCC.[C:27]([O:32][CH2:33][C@@H:34]1[O:36][CH2:35]1)(=O)[CH2:28][CH2:29][CH3:30].C([O-])([O-])=O.[Cs+].[Cs+]>C1COCC1.CC(=O)OCC>[O:32]1[C:27]2[CH:28]=[CH:29][C:30]([N:10]3[CH2:11][C@H:12]([CH2:13][OH:18])[O:8][C:9]3=[O:21])=[CH:23][C:35]=2[O:36][CH2:34][CH2:33]1
A solution of (2,3-dihydro-benzo[1,4]dioxin-6-yl)-carbamic acid benzyl ester (3.0 g, 10.5 mmol, prepared according to method C) in THF (60 mL) was cooled to −78° C. before the dropwise addition of n-BuLi (5.1 mL of a 2.5M solution in hexanes, 1.2 eq.). The mixture was stirred at −78° C. for 1 h and then warmed to −15° C. At this temperature (R)-glycidyl butyrate (1.98 g, 1.2 eq.) was added dropwise. The mixture was stirred at rt overnight. Cs2CO3 (tip of a spatula) was added and the mixture heated at 40° C. until complete conversion. The mixture was diluted with EA and washed with sat. NH4Cl solution and water. The org. layer was dried over MgSO4 and concentrated. Chromatography on SiO2 (Hex/EA 2:1, 1:1) gave the desired intermediate as a beige solid (1.09 g, 41% yield).
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