[CH3:1][O:2][N:3]=[C:4]([C:10]1([O:15][CH2:14][CH2:13][O:12]1)[CH3:11])[C:5]([O:7][CH2:8][CH3:9])=[O:6].[Cl-].[Li+].S(Cl)([Cl:21])(=O)=O.C(OC(C)C)(C)C>C(O)(=O)C.O>[CH3:1][O:2][N:3]=[C:4]([C:10]1([O:12][CH2:13][CH2:14][O:15]1)[CH2:11][Cl:21])[C:5]([O:7][CH2:8][CH3:9])=[O:6]
To a solution of ethyl 2-methoxyimino-3,3-ethylenedioxybutyrate (syn isomer, 30 g) in acetic acid (150 ml) was added lithium chloride (7 g) and the mixture was stirred for 15 minutes at ambient temperature. To the mixture was added dropwise sulfuryl chloride (22.4 g), and the mixture was stirred for one hour at ambient temperature and then allowed to stand for overnight. To the reaction mixture was added water (600 ml) under ice-cooling and stirring, and diisopropyl ether (400 ml) was added thereto and then stirred. The diisopropyl ether layer was separated, and the remaining aqueous layer was further extracted with diisopropyl ether. The diisopropyl ether layer and extract were combined together, washed with water, a saturated aqueous solution of sodium bicarbonate, water and a saturated aqueous solution of sodium chloride in turn, dried over magnesium sulfate and then filtered. The filtrate was concentrated and the residual oil (31.2 g) was distilled under reduced pressure to give ethyl 2-methoxyimino-3,3-ethylenedioxy-4-chlorobutyrate (syn isomer), bp 104°-106° C./0.32-0.35 mmHg.
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