Diethyl Ether → 1-(2-Hydroxy-6-methylphenyl)ethanone

Participants

Reaction Conditions

Reaction Steps

In a solution of 2-methoxy-6-methylbenzoic acid ethyl ester (5 g, 25.77 mmol) and NaOH (6.18 g, 154.64 mmol) in EtOH (100 mL) and water (40 mL) was stirred at reflux for 24 hours. EtOH was then removed using a rotary evaporator and the aqueous was acidified with HCl (1 N) to pH=4. Extract with CH2Cl2 (3×100 mL) followed by concentration using a rotary evaporator afforded 4.25 g, of 2-methoxy-6-methylbenzoic acid (100%) as a white solid. To a solution of 2-methoxy-6-methylbenzoic acid (1.66 g, 10 mmol) in CH2Cl2 (80 mL) at room temperature was added BBr3 in CH2Cl2 (20 mL, 20 mmol). The reaction mixture was stirred at room temperature for 20 hour and then concentrated using a rotary evaporator. The resulting residue was re-dissolved in CH2Cl2 (50 mL), diluted with HCl (0.5 N), extracted with CH2Cl2 (3×100 mL) and concentrated using a rotary evaporator to afford 1.52 g of 2-hydroxy-6-methylbenzoic acid (100%). To a solution of 2-hydroxy-6-methylbenzoic acid (1.52 g, 10 mmol) in THF (50 mL) at room temperature was slowly added CH3Li in ether (22 mL, 35 mmol) and the suspension was stirred at 60° C. for 6 hour. The reaction was quenched with HCl (0.5 N) aqueous and extracted with CH2Cl2 (3×100 mL). Concentration using a rotary evaporator afforded 1 g of 2′-hydroxy-6′-methylacetophenone (67%) as a brown oil. A solution of 2′-hydroxy-6′-methylacetophenone (1.0 g, 6.67 mmol) in CH2Cl2 (50 mL) at room temperature was mixed with isonicotinoyl chloride hydrochloride (2.136 g, 12 mmol) and triethylamine (3.9 mL, 28 mmol) sequentially. The resulting mixture was stirred at room temperature for 2 hours, quenched with water, and extracted with CH2Cl2 (3×100 mL) The volume was reduced using a rotary evaporator to minimal and triturated with hexanes. The solid was collected by filtration to afford 1.2 g of the corresponding isonicotinic aryl ester (70%). A solution of the above isonicotinic aryl ester (1.2 g, 4.70 mmol) in THF (50 mL) was mixed with potassium tert-butoxide (2.24 g, 20 mmol) and stirred at 65° C. for 2hours. The reaction was quenched with water and acidified with HCl (0.5 N) to pH=6. Extract with CH2Cl2 (3×100 mL) followed by concentration using a rotary evaporator afforded a yellow solid residue. It was purified by column (SiO2, hexane/EtOAc=1:1) to provide 0.72 g of the diketone (60%). A solution of the above diketone (0.7 g, 2.745 mmol) in HOAc (50 mL) was stirred at reflux for 2 hours. All the solvent was removed using a rotary evaporator to afford a solid residue. It was then diluted with water and neutralized with NaOH (0.5 N) to pH=8. The solid was collected by filtration and washed with water and hexanes sequentially to afford 0.32 g of 5-methyl-2-(pyridin-4-yl)-4H-chromen-4-one as a light yellow solid (49%).

Provenance & Evidence