Reaktion #506011

Reaktionsgleichung

2-fluoro-4-hydroxybenzoic acid

acetic anhydride

→

2-fluoro-4-acetoxybenzoic acid

Ausbeute 57.0%

Lösungsmittel

pyridine

Reaktionsbedingungen

Aufarbeitung

1. 1
   SonstigeThe pyridine was removed under reduced pressure
2. 2
   workup.DISSOLUTIONthe residue was dissolved in EtOAc (100 mL)
3. 3
   Waschenwashed with 1N HCl (20 mL), water (20 mL)
4. 4
   Trocknendried over anhydrous Na2SO4
5. 5
   SonstigeRemoval of solvent

Vorschrift

To a solution of 2-fluoro-4-hydroxybenzoic acid (1.87 g, 12 mmol) in 30 mL pyridine was added acetic anhydride (1.84 g, 18 mmol) and catalytic amount of DMAP and the reaction mixture was stirred at rt for 15 h. The pyridine was removed under reduced pressure; the residue was dissolved in EtOAc (100 mL), washed with 1N HCl (20 mL), water (20 mL) and dried over anhydrous Na2SO4. Removal of solvent gave 2-fluoro-4-acetoxybenzoic acid in 57% yield (1.35 g). To a suspension of 2-fluoro-4-acetoxybenzoic acid (1.33 g, 6.71 mmol) in 10 mL anhydrous dichloromethane was added oxalyl chloride (2.56 g, 20.13 mmol). Two drops of DMF was added and the reaction mixture was stirred at rt for 3 h. The solvent and excess oxalyl chloride were removed under reduced pressure to give 1.48 g of 2-fluoro-4-acetoxybenzoyl chloride which was used in next step without purification. To a solution of 2′-hydroxyacetophenone (0.93 g, 6.83 mmol) in 15 mL anhydrous pyridine was added 2-fluoro-4-acetoxybenzoyl chloride (1.48 g, 6.83 mmol) and the reaction mixture was stirred at rt for 15 h under nitrogen atmosphere. Then the reaction mixture was poured into 100 mL 2N HCl, extracted with EtOAc (200 mL). The crude compound was purified by column chromatography (Silica Gel 230-400 mesh; 20% EtOAc in hexanes as eluent) to give 4-acetoxy-2-fluorobenzoic acid 2-acetyl phenyl ester (1.14 g, 53%). The ester compound (0.74 g, 2.34 mmol) was dissolved in 10 mL anhydrous THF. Potassium tert-butoxide (0.53 g, 4.68 mmol) was added in portions and stirred at rt under nitrogen for 1 h. A yellow solid was formed. The reaction mixture was quenched with 15 mL saturated aqueous ammonium chloride. EtOAc (100 mL) was added and the organic phase was separated and dried over anhydrous Na2SO4. Removal of solvent gave crude product (0.725 g) which was used in next step without further purification. This crude compound (0.72 g, 2.62 mmol) was dissolved in 10 mL glacial AcOH, conc. HCl (1 mL) was added and the reaction mixture was stirred at 110° C. for 4 h. The reaction mixture was cooled to rt. The solid was isolated by filtration, washed with AcOH and dried under vacuum to give 126 mg (21%) over 2 steps. MS (ES) m/z: 256.89 (M), 255.86 (M−1); Mp. 287-289° C.

Quelle