[F:1][C:2]1[CH:7]=[CH:6][C:5]([S:8]([NH:11][C@@H:12]([C:14]([OH:16])=[O:15])[CH3:13])(=[O:10])=[O:9])=[CH:4][CH:3]=1.[CH2:17]=[C:18]([CH3:20])[CH3:19].S(=O)(=O)(O)O.C(=O)(O)[O-].[Na+]>O1CCOCC1.C(Cl)Cl>[F:1][C:2]1[CH:3]=[CH:4][C:5]([S:8]([NH:11][C@@H:12]([C:14]([O:16][C:18]([CH3:20])([CH3:19])[CH3:17])=[O:15])[CH3:13])(=[O:9])=[O:10])=[CH:6][CH:7]=1A solution of N-[(4-fluorophenyl)sulfonyl]-D-alanine from Example 3a (8.00 g, 32.4 mmol), isobutene (120 mL), and concentrated sulfuric acid (0.5 mL) in 1,4-dioxane (20 mL) and CH2Cl2 (60 mL) was added to a 500 mL high pressure bottle and sealed. The mixture was shaken at room temperature for 95 hours at a pressure of 18 psi. The mixture was poured into an aqueous solution containing 20 g of sodium bicarbonate, which was cooled by an ice bath. The aqueous solution was extracted with ethyl acetate and the combined organic layers were washed successively with water and brine, dried with MgSO4, and concentrated to a clear, yellow oil (6.06 g). Chromatography on silica gel (20% ethyl acetate in hexane) afforded N-[(4-fluorophenyl)sulfonyl]-D-alanine, 1,1-dimethylethyl ester, as a white solid (5.00 g, 51% yield): Anal. calc'd for C13H18NO4FS: C, 51.47; H, 5.98; N, 4.62. Found: C, 51.39; H, 5.82; N, 4.53.
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