Step D: Preparation of ethyl 6-chloro-2-pyridinecarboxylate: 6-chloro-2-pyridinecarboxylic acid (23.5 g, 149 mmol), anhydrous ethanol (100 mL), and toluene (400 mL) were added to a round-bottomed flask equipped with a condenser. Concentrated sulfuric acid (4 mL) was slowly added to the reaction system, followed by heating the mixture to reflux and maintaining the reaction for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature. The solvent was removed by distillation under reduced pressure and the resulting oily product was dissolved in ethyl acetate (200 mL), washed with 10% aqueous potassium carbonate and dried over anhydrous sodium sulfate. Finally, the dried organic phase was concentrated under reduced pressure to afford ethyl 6-chloro-2-pyridinecarboxylate (26 g, 94% yield).
[1] Patent: WO2012/82689, 2012, A1. Location in patent: Page/Page column 56
[2] European Journal of Organic Chemistry, 2014, vol. 2014, # 28, p. 6295 - 6302
[3] Organic Letters, 2014, vol. 16, # 15, p. 3860 - 3863
