Cl[S:2]([CH2:5][C@H:6]([CH3:17])[C:7]([O:9][CH2:10][C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:8])(=[O:4])=[O:3].[CH3:18][NH:19][CH3:20]>C(Cl)Cl>[CH3:18][N:19]([CH3:20])[S:2]([CH2:5][C@H:6]([CH3:17])[C:7]([O:9][CH2:10][C:11]1[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=1)=[O:8])(=[O:4])=[O:3]A 100 mL round bottomed flask equipped with magnetic stir bar was charged with 1.7 g benzyl 3-chlorosulfonyl-2(R)-methylpropionate from Example 3 in 25 mL CH2Cl2. The solution was cooled to −78° C. and 15 mL of anhydrous dimethylamine was slowly added. After 30 minutes the reaction was concentrated in vacuo and the residue was partioned between EA/H2O. The organic phase was dried, concentrated in vacuo to yield 1.4 g of benzyl 3-[(dimethylamino)sulfonyl]-2(R)-methylpropionate as a clear amber oil which was used directly in the next step.
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