O[CH2:2][CH2:3][NH:4][C:5]([CH2:11][C:12]([O:14][CH3:15])=[O:13])=[CH:6][C:7]([O:9][CH3:10])=[O:8].C(N(CC)CC)C.[CH3:23][S:24](Cl)(=[O:26])=[O:25]>O>[CH3:23][S:24]([CH2:2][CH2:3][NH:4][C:5]([CH2:11][C:12]([O:14][CH3:15])=[O:13])=[CH:6][C:7]([O:9][CH3:10])=[O:8])(=[O:26])=[O:25]The solution of dimethyl 3-(2-hydroxyethylamino)-2-pentenedioate was cooled to 0° C., and triethylamine (235 mL, 170.6 g, 1.69 mol) was added in one portion. Methanesulfonyl chloride (168.8 g, 1.47 mol) was added dropwise via an addition funnel over 3.75 hours, with the temperature rising to 5°-7° C. The medium-yellow slurry darkened to yellow-orange as the last 10 mL methanesulfonly chloride was added. The mixture was stirred at 0° C. for an additional 2 hours, and water (250 mL) added. The organic phase was washed with water (4×500 mL) and brine (250 mL), and dried overnight over anhydrous magnesium sulfate. Afer filtration, the solvents were evaporated on a rotary evaporator under reduced pressure at 50° C. to afford 310.0 g (93% yield) of dimethyl 3-(2-methanesulfonylethylamino)-2-pentenedioate as a red oil. The mesylenamine may be purified at this point, if necessary or desired, and may be converted to the haloenamine by the following method or used directly in Step 2, Alternate II.
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