[S:1]1(=[O:12])(=[O:11])[C:6]2[S:7][CH:8]=[CH:9][C:5]=2[CH:4]([OH:10])[CH2:3][NH:2]1.C1(C)C=CC(S(O)(=O)=O)=CC=1.[CH:24]([O:26][CH2:27][CH3:28])=[CH2:25].C(=O)(O)[O-].[Na+].[CH2:34]1[CH2:38][O:37][CH2:36][CH2:35]1>>[CH2:24]([O:26][CH:27]([O:10][CH:4]1[C:5]2[CH:9]=[CH:8][S:7][C:6]=2[S:1](=[O:12])(=[O:11])[N:2]([CH:36]([O:37][CH2:38][CH3:34])[CH3:35])[CH2:3]1)[CH3:28])[CH3:25]A solution of the product from Step C (106.9 g, 0.521 mol) in THF (360 mL) was cooled to 0° C. and para-toluenesulfonic acid (3.6 g) was added. Ethyl vinyl ether (250 mL, 2.6 mol) was added over a period of 1.75 hr while maintaining the temperature of the reaction mixture below 5° C. The yellow solution was stirred at 0° C. for 1 hr, a saturated aqueous sodium bicarbonate solution (400 mL) was added and this mixture was extracted with ethyl acetate (3×250 ml). The combined extracts were dried (Na2SO4) and evaporated to give a residue which was purified by column chromatography (silica, hexane to 20% hexane/ethyl acetate) to give the desired product (78%) as a light yellow oil. This material was used in the next step.
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