Di-tert-butyl dicarbonate → Methyl 2-(bis((tert-butoxy)carbonyl)amino)prop-2-enoate

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To a solution of 2-tert-butoxycarbonylamino-3-hydroxy-propionic acid methyl ester (10.0 g, 39 mmol) and di-tert-butyl-dicarbonate (21.8 g, 2.6 equiv.) in acetonitrile (40 mL) was added 4-dimethylaminopyridine (0.48 g, 0.1 equiv) at room temperature. The solution was stirred overnight and concentrated. The residue was dissolved in diethyl ether, washed sequentially with 1 M potassium hydrogen sulfate (2×), saturated sodium bicarbonate, brine, dried over magnesium sulfate, and concentrated to give 15.6 g (quant.) as an oil. Inspection of the 1H NMR showed a mixture of the title compound and 2-(di-tert-butoxycarbonylamino)-3-tert-butoxycarbonyloxy-propionic acid methyl ester. As it was later found that both react with secondary amines to give the same products, the mixture was used without separation. 2-(Di-tert-butoxycarbonylamino)-acrylic acid methyl ester: 1H-NMR (CDCl3) δ 1.45 (s, 18H), 3.78 (s, 3H), 5.63 (s, 1H), 6.33 (s, 1H). Mass spec.: 324.14 (M+Na)+. 2-(Di-tert-butoxycarbonylamino)-3-tert-butoxycarbonyloxy-propionic acid methyl ester: 1H-NMR (CDCl3, 500 MHz) δ 1.46 (s, 9H), 1.49 (s, 18H), 3.72 (s, 3H), 4.42 (dd, J=11.6, 9.2, 1H), 4.75 (dd, J=11.3, 4.6, 1H), 5.30 (dd, J=9.2, 4.6, 1H). Mass spec.: 442.21 (M+Na)+.

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