F[B-](F)(F)F.[CH2:6]([O+](CC)CC)[CH3:7].[F-].[C:14]([C:17](=[N:22][O:23][CH2:24][CH3:25])[C:18]([O:20][CH3:21])=[O:19])(=[O:16])[NH2:15].C(N(CC)CC)C>C(Cl)Cl.O>[NH:15]=[C:14]([O:16][CH2:6][CH3:7])[C:17](=[N:22][O:23][CH2:24][CH3:25])[C:18]([O:20][CH3:21])=[O:19]To a solution of Meerwein reagent (triethyloxonium tetrafluoroborate) {prepared from bron fluoride etherate (2.84 g) by a method of Org. Syn., 46, 113 (1966)} in methylene chloride (30 ml) was added methyl 2-carbamoyl-2-ethoxyiminoacetate (syn isomer, 2.6 g) and the mixture was stirred for 18 hours at room temperature. The reaction mixture was cooled in an ice-bath and triethylamine (3 g) was added thereto, followed by an addition of water (20 ml). The organic layer was separated out, dried over magnesium sulfate and evaporated to give crude methyl 3-imino-3-ethoxy-2-ethoxyiminopropionate (syn isomer) (5.0 g) as an oil. ##STR15##
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