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(S)-3-{(R)-2-[4-(3,4-Dichloro-benzyloxy)-phenyl]-2,3-dihydro-benzo[1,4]dioxin-6-yl}-2-(4-nitro-benzenesulfonylamino)-propionic acid methyl ester (1.7 g) was dissolved in 10 mL dry THF and 1320 mg triphenylphosphine and 691 μL (R)-(+)-1-phenyl-1-propanol were added. The mixture was stirred at 0° C. for 10 minutes, then 992 μL DIAD was added dropwise. The reaction was stirred at room temperature for 3 hours and was evaporated. The residue was purified by silica gel flash chromatography (hexanes to 8:2 hexanes/EtOAc). The resulting residue was dissolved in 20 mL dry DMF, then 526 μL mercaptoacetic acid and 2.5 mL DBU were added at room temperature. The reaction was stirred for 30 minutes and was partitioned between saturated aqueous NaHCO3 and diethyl ether. The aqueous layer was washed again with diethyl ether and the organic layers were combined. The organic layer was washed with aqueous NaHCO3, dried over Na2SO4 and evaporated. The residue was purified by silica gel flash chromatography (hexanes to 8:2 hexanes/EtOAc (first column)) and (hexanes to 1:1 DCM-hexanes to DCM to 9:1 DCM-EtOAc (second column)) to give 1.05 g of the product after drying.

1. stirringThe reaction was stirred at room temperature for 3 hours
2. customwas evaporated
3. customThe residue was purified by silica gel flash chromatography (hexanes to 8:2 hexanes/EtOAc)
4. dissolutionThe resulting residue was dissolved in 20 mL dry DMF
5. addition526 μL mercaptoacetic acid and 2.5 mL DBU were added at room temperature
6. stirringThe reaction was stirred for 30 minutes
7. customwas partitioned between saturated aqueous NaHCO3 and diethyl ether
8. washThe aqueous layer was washed again with diethyl ether
9. washThe organic layer was washed with aqueous NaHCO3
10. dry with materialdried over Na2SO4
11. customevaporated
12. customThe residue was purified by silica gel flash chromatography (hexanes to 8:2 hexanes/EtOAc (first column)) and (hexanes to 1:1 DCM-hexanes to DCM to 9:1 DCM-EtOAc (second column))