[C:1]([NH:5][S:6]([C:9]1[CH:14]=[CH:13][C:12]([CH2:15][CH2:16][CH3:17])=[CH:11][CH:10]=1)(=[O:8])=[O:7])([CH3:4])([CH3:3])[CH3:2].[Li]CCCC.[B:23](OC(C)C)([O:28]C(C)C)[O:24]C(C)C.Cl>C1COCC1>[C:1]([NH:5][S:6]([C:9]1[CH:10]=[CH:11][C:12]([CH2:15][CH2:16][CH3:17])=[CH:13][C:14]=1[B:23]([OH:28])[OH:24])(=[O:7])=[O:8])([CH3:4])([CH3:3])[CH3:2]To a solution of 2.85 g (11.2 mmol) of N-t-butyl-4-n-propylbenzenesulfonamide (from Step A) in anhydrous THF (20 mL) cooled to -40° C. under N2 was added 2.5M n-BuLi solution (11.2 mL, 2.5 equiv). The mixture was warmed to room temperature and stirred for 2 hours. To the mixture, containing the bright red dianion at 0° C., was added triisopropyl borate (3.9 mL, 1.5 equiv). The next day, 2N HCl (3 mL) was added and the mixture was stirred for 1 hour. The solvent was removed under reduced pressure and the residue was extracted with ethyl acetate. The organic solution was washed with 2N HCl, H2O and brine. The organic phase was dried over anhydrous MgSO4 and concentrated in vacuo to afford the titled compound; Rf =0.5 (1:1 EtOAc-hexane). The material was used in the next step without further purification.
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