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11. Sodium (5E)-6-(dimethylamino)-1-ethoxy-5-(ethoxycarbonyl)-1,4-dioxohexa-2,5-dien-2-olate. A mixture
of ethyl 2-(dimethylamino)methylene-3-oxobutanoate (3.0 g, 16.2 mmol), diethyl oxalate (2.84 g, 17.3
mmol) and NaH (60% dispersion in oil) (0.84 g, 21.0 mmol) in THF (45 mL) was refluxed for 5 h. After
cooling, the solid that formed was filtered, washed with THF (10 mL), and dried. Yield 3.22 g (64%),
1
mp 220 °C (dec.), beige powder. IR (ATR): 2982, 1709, 1689, 1663, 1571 cm–1; H NMR (400 MHz,
DMSO-d6) δ 1.14 (br t, J = 7.0 Hz, 3H, Me), 1.20 (t, J = 7.0 Hz, 3H, Me), 2.88 (s, 6H, NMe2), 3.97 (br q,
J = 7.0 Hz, 2H, CH2O), 4.05 (q, J = 7.0 Hz, 2H, CH2O), 5.65 (s, 1H, =CH), 7.14 (br s, 1H, =CHN).
Diethyl
4-oxo-4H-pyran-2,5-dicarboxylate
(1).
Sodium (5E)-6-(dimethylamino)-1-ethoxy-5-
(ethoxycarbonyl)-1,4-dioxohexa-2,5-dien-2-olate (3.0 g, 9.76 mmol) was dissolved in H2O (10 mL) and
quenched with concentrated HCl (3 mL) at 0 °C (ice bath) for 30 min. The product 1 was extracted with
9