Example 1, Synthesis of diethyl pyridine-2,3-dicarboxylate: alkyne propylamine (0.2 mmol), diethyl butynedioate (34 g, 0.2 mmol) and ethanol (100 mL) were added to a 250 mL reaction flask, and 50% hydrogen peroxide (~26 mL, 0.30 mmol) was added with stirring. The reaction mixture was heated to 65 °C and kept for 12 h. The progress of the reaction was monitored by TLC (unfolding agent: petroleum ether/ethyl acetate = 2:1, v/v) until the complete disappearance of diethyl butynedioate. After completion of the reaction, ethanol was recovered by atmospheric distillation. Water (100 mL) was added to the residue and the mixture was extracted with ethyl acetate (50 mL x 3). The organic layer (upper layer) was combined and washed sequentially with water (50 mL) and saturated brine (50 mL). After recovery of ethyl acetate by atmospheric distillation, a reduced pressure distillation (6 mmHg) was carried out and the fraction at 165-170 °C/6 mmHg was collected to give diethyl pyridine-2,3-dicarboxylate (36.6 g, 82% yield).
