Diethyl acetylenedicarboxylate → 3-Oxo-5H-pyrimido[2,1-c][1,4]benzoxazine-1-carboxylic Acid, Ethyl Ester

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A solution of the compound of formula II, 3-amino-2H-1,4-benzoxazine(1.75 g, 11.08 mmol, described in Example 3) and diethyl acetylenedicarboxylate (2.2g, 12.9 mmol) dissolved in ethanol (30 ml) was stirred at room temperature for 21/2 hours. The precipitate was collected to give 1.30 g of the title compound as colourless crystals; mp 174°-175° C. (after recrystallization from ethyl acetate-hexane); IR(CHCl3) 1738, 1650 cm-1 ; NMR(CDCl3)δ1.2 (t, J=7Hz, 3H), 4.3(q,J=7Hz, 2H), 4.92 (s, 3H), 6.68 (s,1H), 7.3 (m,4H); M+ 272; Anal. Calc'd: C, 61.76%; H, 4.44%; N, 10.29%; Found: C, 61.99%; H, 4.35%; N, 10.32%.

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