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With thionyl chloride In DMF (N,N-dimethyl-formamide)Heating / reflux
The third step of Scheme 4: To a 25 mL thionyl chloride suspension of 5-nitro-2-hydroxynicotinic acid methyl ester (4.62 g, 23.3 mmole) was added 1 mL DMF and the mixture heated to reflux until the reaction was complete as judged by TLC. The thionyl chloride was evaporated under reduced pressure and azeotroped twice with toluene. The resulting yellow semi-solid was cooled in an ice bath and treated with 50 mL MeOH. It was stirred for 20 minutes and then poured into 200 mL water, extracted with EtOAc (2*150 mL) and the combined organics washed with dilute aqueous NaOH, water, brine and dried over MgSO4. 5.03 g (99percent) of 2-chloro-5-nitronicotinic acid methyl ester was obtained as a yellow oil. 1H NMR (400 MHz, CHLOROFORM-D) 8 ppm 4.04 (s, 3H) 8.94 (d, J=2.78 Hz, 1H) 9.33 (d, J=2.78 Hz, 1H).
2-Hydroxy-5-nitronicotinic acid (29 g; 0.16 moles) was added portionwise to phosphorus oxychloride (90 ml) with stirring. The temperature was raised to 100 0C and heating continued for 3 hours before cooling to room temperature. The bulk of the solvent was removed before adding to ice-cold methanol (100 ml). The mixture was basified to pH 9 with saturated sodium bicarbonate solution and extracted with dichloromethane. The organic phase was dried (sodium sulphate), filtered and evaporated before purification by dry flash chromatography on silica gel. Methyl 2- chloro-5-nitronicotinate was eluted with 67percent ethyl acetate in heptane (31 g, 90percent).
With thionyl chloride; In DMF (N,N-dimethyl-formamide);Heating / reflux;
The third step of Scheme 4: To a 25 mL thionyl chloride suspension of 5-nitro-2-hydroxynicotinic acid methyl ester (4.62 g, 23.3 mmole) was added 1 mL DMF and the mixture heated to reflux until the reaction was complete as judged by TLC. The thionyl chloride was evaporated under reduced pressure and azeotroped twice with toluene. The resulting yellow semi-solid was cooled in an ice bath and treated with 50 mL MeOH. It was stirred for 20 minutes and then poured into 200 mL water, extracted with EtOAc (2*150 mL) and the combined organics washed with dilute aqueous NaOH, water, brine and dried over MgSO4. 5.03 g (99%) of 2-chloro-5-nitronicotinic acid methyl ester was obtained as a yellow oil. 1H NMR (400 MHz, CHLOROFORM-D) 8 ppm 4.04 (s, 3H) 8.94 (d, J=2.78 Hz, 1H) 9.33 (d, J=2.78 Hz, 1H).
With potassium carbonate; In DMF (N,N-dimethyl-formamide); at 20℃;
The fourth step of Scheme 4: To a 5 mL DMF solution of <strong>[190271-88-6]2-chloro-5-nitronicotinic acid methyl ester</strong> (269 mg, 1.25 mmole) was added methyl thioglycolate (111 muL, 1.25 mmole) followed by potassium carbonate (428 mg, 3.1 mmole) and the mixture was stirred at room temperature overnight. The reaction mixture was then poured into 50 mL water and extracted with CH2Cl2. The aqueous phase was acidified with 2N HCl and extracted with CH2Cl2. Combined organic phases were washed with water and dried over MgSO4. The solids were removed by filtration and the solvent was evaporated under reduced pressure to give 240 mg (76%) 3-hydroxy-5-nitro-thieno[2,3-b]pyridine-2-carboxylic acid methyl ester as a tan colored solid. 1H NMR (400 MHz, CHLOROFORM-D) delta ppm 4.02 (s, 3H) 9.01 (d, J=2.53 Hz, 1H) 9.52 (d, J=2.53 Hz, 1H) 10.19 (s, 1H).
2-Hydroxy-5-nitronicotinic acid (29 g; 0.16 moles) was added portionwise to phosphorus oxychloride (90 ml) with stirring. The temperature was raised to 100 0C and heating continued for 3 hours before cooling to room temperature. The bulk of the solvent was removed before adding to ice-cold methanol (100 ml). The mixture was basified to pH 9 with saturated sodium bicarbonate solution and extracted with dichloromethane. The organic phase was dried (sodium sulphate), filtered and evaporated before purification by dry flash chromatography on silica gel. Methyl 2- chloro-5-nitronicotinate was eluted with 67% ethyl acetate in heptane (31 g, 90%).
With potassium carbonate; In N,N-dimethyl-formamide; at 20 - 80℃;
<strong>[190271-88-6]2-Chloro-5-nitro-nicotinic acid methyl ester</strong> (578 mg, 2.44 mmol) and n-propyl hydrazine oxalate (400 mg, 2.44 mmol) in DMF (10 ml) was treated with K2CO3 (672 mg, 4.87 mmol). The mixture was stirred at 80 C. for 3 hr and then at RT overnight. The reaction mixture was then concentrated and diluted with EtOAc. The organic layer was partitioned over water and solid citric acid was added to acidify the mixture to pH 1. The organic layer was washed with brine, dried over Na2SO4 and concentrated to dryness. The solid obtained was triturated with CH2Cl2 and then hexanes to afford the product, 5-nitro-1-propyl-1,2-dihydro-pyrazolo[3,4-b]pyridin-3-one (405 mg, Yield: 75%). LCMS calcd for C9H10N4O3 (m/e) 222, obsd. 223 (M+H).
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