Imidazole → Acetophenone

Ethyl 2-chloronicotinate (11.14 g, 60 mmol) was dissolved in anhydrous methanol (60 mL). Sodium methoxide (18 mL, 25 wt % in methanol) was added slowly at room temperature under nitrogen. The reaction mixture was stirred under reflux for 15 hours. Methanol was removed under vacuum. The residue was dissolved in ethyl acetate (200 mL). The organic layer was washed with a saturated aqueous NH4Cl solution (1×100 mL) and brine (50 mL), and dried over anhydrous Na2SO4—Removal of solvent gave ethyl-2-methoxynicotinate (9.88 g, 91%) as yellow oil. To a solution of 3,5-dimethyl-4-hydroxyacetophenone (2.46 g, 15 mmol) in anhydrous DMF (75 mL) were added imidazole (3.27 g, 48 mmol) and tert-butyldimethylsilylchloride (2.7 g, 18 mmol). The reaction mixture was stirred at room temperature under nitrogen for 15 hours. Water (200 mL) was added. The mixture was extracted with ethyl acetate (200 mL). The organic layer was washed with water (2×100 mL) and brine (100 mL), and dried over anhydrous Na2SO4. Removal of solvent gave 3,5-demthyl-4-tert-utyldimethylsilyloxy acetophenone as a colorless oil in quantitative yield (4.4 g). To a stirred solution of 3,5-demthyl-4-tert-butyldimethylsilyloxy acetophenone (1.58 g, 5.6 mmol) in anhydrous THF (15 mL) was added lithium bis(trimethylsilyl)amide (6.8 mL, 1.0 M solution in THF) at −40° C. under nitrogen over a period of 15 min. Stirring was continued at −40° C. for 15 min. A solution of ethyl-2-methoxynicotinate in anhydrous THF (15 mL) was added slowly. Stirring was continued at −40° C. for 10 min, then allowed to warm to room temperature. Stirring was continued for another 15 h at room temperature. The reaction mixture was diluted with ethyl acetate (200 mL). A saturated aqueous NH4Cl solution (50 mL) was added. The organic layer was separated and dried over anhydrous Na2SO4. Removal of solvent gave the desired crude compound (2.4 g) which was used in next step without purification. The above compound (2.31 g, 5.6 mmol) and pyridinium hydrochloride (6.47 g, 56 mmol) was mixed together and stirred at 190° C. for 3 hours. The mixture was cooled to room temperature. Water (100 mL) was added. The solid was isolated, washed with water and dried under vacuum. The crude product was purified by column chromatography (SilicaGel 230-400 mesh; 2% methanol in CH2Cl2 as eluent) to give the desired intermediate (0.598 g, 40% over two steps) as an off-white solid. To a solution of the desired intermediate (0.53 g, 2.0 mmol) in anhydrous DMF (10 mL) sodium hydride (0.88 g, 2.2 mmol) was added in portions. The reaction mixture was stirred at room temperature for 10 min. Ethyl-2-bromo acetate (0.367 g, 2.2 mmol) was added and stirring was continued at room temperature for 15 h under nitrogen. Water (30 mL) was added, and the solid was filtered off, washed with water and dried under vacuum to give [2,6-dimethyl-4-(4-oxo-4H-pyrano[2,3-b]pyridin-2-yl)phenoxy]acetic acid ethyl ester (0.69 g, 97%). The above compound (0.35 g, 1.0 mmol) was suspended in THF (10 mL). An, aqueous solution of sodium hydroxide (0.08 g, 2.0 mmol) in water (1 mL) was added and the mixture was stirred at room temperature for 24 h (progress of the reaction was monitored by TLC). The solvent was evaporated to dryness. The crude compound was washed with THF. The residue was dissolved in water (10 mL) and acidified to pH ˜2. The formed precipitate was filtered off and dried under vacuum the crude compound was purified by column chromatography (Silica Gel 230-400 mesh; 5% MeOH in CH2Cl2 as eluent) to give 2-(2,6-dimethyl-4-(4-oxo-4H-pyrano[2,3-b]pyridin-2-yl)phenoxy)acetic acid (0.21 g, 64%) as pale yellow solid; MS (ES) m/z: 326.91 (M+1), 325.90 (M); MP 280° C. at decomposition.

1. extractionThe mixture was extracted with ethyl acetate (200 mL)
2. washThe organic layer was washed with water (2×100 mL) and brine (100 mL)
3. dry with materialdried over anhydrous Na2SO4
4. customRemoval of solvent

ORD record

ord-f0a5cf621a01480b91c5d92e74b77e30

Source dataset

uspto-grants-2013_04

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US08410109B2