Cesium carbonate → (S)-3-(2,3-dihydro-benzo[1,4]dioxin-6-yl)-5-hydroxymethyl-oxazolidin-2-one

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A solution of (2,3-dihydro-benzo[1,4]dioxin-6-yl)-carbamic acid benzyl ester (13.0 g, 45.6 mmol) in THF (220 mL) was cooled to −78° C. before the drop wise addition of n-BuLi (29.5 mL of a 2.36M solution in hexanes, 1.1 eq). The mixture was stirred at −78° C. for 1 h and then warmed to −15° C. At this temperature (S)-glycidyl butyrate (7.37 g, 1.1 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 a sat. aq. NH4Cl and water. The org. layer was dried over MgSO4 and concentrated. The residue was purified by CC (Hex/EA 2:1, 1:1) to afford the title intermediate as a grey solid (7.04 g, 62% yield).

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