Triethyl 1,2,4-triazine-3,5,6-tricarboxylate and 2,3,6-Tricarboethoxypyridine could be produced through the following synthetic routes.

A. Ethyl thioamidooxalate. A 100-mL, round-bottomed flask is fitted with a magnetic stirring bar. Ethyl cyanoformate (20 g, 0.20 mol) in benzene (25 mL) is added to the reaction vessel and the mixture is cooled to 0°C with an ice bath. (0.4 g, 5.5 mmol, 0.57 mL) is added to the stirring reaction mixture (0°C) and sulfide is then bubbled into the reaction for an additional 15–20 min. The reaction mixture is allowed to stir at 25°C (14–16 hr). The crude product is collected by filtration and washed with benzene (2 × 3 mL) to give 20.96 g (78%) of pure ethyl thioamidooxalate. The filtrate is concentrated under reduced pressure and the crude product subjected to chromatography on silica gel (30% ether–hexane eluant) to give an additional 1.57 g of ethyl thioamidooxalate. The total amount of ethyl thioamidooxalate isolated as a bright-yellow solid is 22.53 g (84%); mp 63–66°C.

B. Ethyl oxalamidrazonate. A 1-L, round-bottomed flask is equipped with a magnetic stirring bar and fitted with a 125-mL addition funnel. A solution of anhydrous hydrazine (4.8 g, 0.15 mol) in ethanol (75 mL) is added dropwise (10 min) to a stirred solution of ethyl thioamidooxalate (20.0 g, 0.15 mol) in ethanol (450 mL) at 25°C. The reaction mixture is stirred at 25°C (3.0 hr). The solvent is removed under reduced pressure and the reddish-orange solid is triturated with ethanol (350 mL). The ethanolic solution containing the oxalamidrazonate is concentrated under reduced pressure to afford 13.90 g (71%) of ethyl oxalamidrazonate as a yellow solid .

C. Diethyl dioxosuccinate (CAS NO.: ). A 1-L, round-bottomed flask equipped with a magnetic stirring bar is charged with dihydroxytartaric acid disodium salt hydrate (100 g, 0.44 mol) and absolute ethanol (750 mL). The suspension is cooled to 0°C with an ice bath and anhydrous hydrogen chloride gas is bubbled into the reaction mixture with stirring (0°C, ca. 30 min). The reaction mixture is stoppered and placed in the refrigerator for 72 hr. The mixture is filtered using a Büchner funnel and the filtrate is concentrated under reduced pressure. The crude diethyl dioxosuccinate is distilled under reduced pressure to afford 39.60 g (44%) of pure diethyl dioxosuccinate is, bp 109–116°C (6–8 mm); lit. bp 109–114°C (6 mm).

D. Triethyl 1,2,4-triazine-3,5,6-tricarboxylate (CAS NO.: ). A 1-L, three-necked, round-bottomed flask is equipped with a magnetic stirring bar, a 500-mL addition funnel, and a nitrogen inlet. A solution of ethyl oxalamidrazonate (11.6 g, 88.0 mmol) in absolute ethanol (350 mL) is added dropwise (40–45 mi) to a stirring solution of diethyl dioxosuccinate (23.1 g, 114.0 mmol) in absolute ethanol (86 mL) at 25°C under nitrogen. After the addition is complete, the reaction mixture is stirred at 25°C (16 hr). A reflux condenser is fitted onto the three-necked, round-bottomed flask and the reaction mixture is warmed at reflux for 2.0 hr. The reaction mixture is cooled and the solvent is removed under reduced pressure. Purification of the product is effected by gravity chromatography on a 5.20 × 40.0-cm column of silica gel (10–40% ether–hexane gradient elution), collecting 100-mL fractions. The fractions are analyzed by thin-layer chromatography on silica gel (40% ether–hexane eluant). The fractions containing product are combined and the solvent is removed under reduced pressure to afford 14.70 g (56%) of pure triethyl 1,2,4-triazine-3,5,6-tricarboxylate as a viscous, yellow oil.

E. 2,3,6-Tricarboethoxypyridine (CAS NO.: ). A 50-mL, round-bottomed flask is fitted with a magnetic stirring bar and a reflux condenser. Triethyl 1,2,4-triazine-3,5,6-tricarboxylate (1.49 g, 5.0 mmol) and chloroform (22.7 mL) are added to the reaction vessel. N-Vinyl-2-pyrrolidone (2.22 g, 20 mmol, 2.3 mL) is added to the solution and the reaction mixture is warmed at 60°C under an atmosphere of nitrogen for 26 hr. The solvent is removed under reduced pressure and the crude product subjected to gravity chromatography on a 2.7 × 32-cm column of silica gel (40–50% ether–hexane gradient elution), collecting 50-mL fractions. The fractions are analyzed by thin-layer chromatography on silica gel (50% ether–hexane eluant). The fractions containing product are combined and the solvent is removed under reduced pressure to afford 1.01–1.35 g (68–92%) of 2,3,6-tricarboethoxypyridine as a yellow oil.

Notice: is highly toxic and a stench. Steps A and B must be run in an efficient fume hood.