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Step 2: Preparation of methyl 5-chloro-4-nitrothiophene-2-carboxylate Fuming nitric acid (15 mL) was placed in an ice bath and cooled with saturated brine. Methyl 5-chlorothiophene-2-carboxylate (4.99 g, 28.3 mmol) was added slowly in small batches to avoid violent reaction. After addition, the reaction mixture was stirred in an ice bath for 1 hour. Upon completion of the reaction, the mixture was poured into ice water and a solid was precipitated. The precipitate was collected by filtration, washed with water and dried under vacuum to afford methyl 5-chloro-4-nitrothiophene-2-carboxylate (3.88 g, 58% yield). The product was characterized by 1H-NMR (400 MHz, DMSO-d6): δ 8.17 (1H, s).