[Br:1][C:2]1[C:11]([CH3:12])=[C:10]2[C:5]([CH2:6][CH2:7][CH2:8][C:9]2=O)=[C:4]([CH3:14])[CH:3]=1.[CH2:15]([SH:18])[CH2:16][SH:17].B(F)(F)F.CCOCC.[OH-].[Na+]>C(Cl)Cl>[Br:1][C:2]1[C:11]([CH3:12])=[C:10]2[C:5]([CH2:6][CH2:7][CH2:8][C:9]32[S:18][CH2:15][CH2:16][S:17]3)=[C:4]([CH3:14])[CH:3]=1To a mixture of 20.0 g of the title compound of Step A in 500 mL of methylene chloride was added 11.2 mL of 1,2-ethanedithiol (purchased from Aldrich Chemical Co.) and 17.0 mL of boron trifluoride diethyl etherate (purchased from Janssen Chimica). The mixture was stirred at room temperature for 3 h. To this reaction mixture was added 15% aqueous sodium hydroxide and the resulting mixture was extracted with methylene chloride. The combined organic extracts were dried over MgSO4, filtered, and concentrated under reduced pressure to afford 20.2 g of the title compound of Step B as a white solid melting at 164°-165° C. 1H NMR (CDCl3): δ 1.98 (m, 2H), 2.15 (s, 3H), 2.38 (m, 2H), 2.58 (t, 2H), 2.78 (s, 3H), 3.40-3.60 (m, 4H), 7.35 (s, 1H).
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