反应详情

温度

80 °C

To an ice-cooled solution of 5-ethyl-4-hydroxy-3-methylbenzaldehyde (10.0 g, 60.9 mmol) in DCM (50 mL) and pyridine (15 mL), trifluoromethanesulfonic acid anhydride (18.9 g, 67 mmol) is added over a period of 20 min. Upon complete addition, the ice bath is removed and the reaction is stirred for further 2 h at rt. The mixture is diluted with DCM (150 mL), washed three times with water, dried over MgSO4, filtered and evaporated. The residue is purified by flash chromatography on silica gel eluting with heptane:EA 9:1 to give trifluoro-methanesulfonic acid 2-ethyl-4-formyl-6-methyl-phenyl ester (10.75 g) as a pale yellow oil; LC-MS: tR=1.07 min; 1H NMR (CDCl3): δ 9.98 (s, 1H), 7.70 (s, 1H), 7.66 (s, 1H), 2.85 (q, J=10.1 Hz, 2H), 2.48 (s, 3H), 1.30 (t, J=10.2 Hz, 3H). b) To a stirred solution of the above triflate (10.7 g, 36.1 mmol) in dry DMF (75 mL) is sequentially added triethylamine (7.3 g, 72.2 mmol), methyl acrylate (31.1 g, 361 mmol), DPPP (819 mg, 1.99 mmol) and Pd(OAc)2 (405 mg, 1.81 mmol) under nitrogen. The mixture is stirred at 115° C. for 5 h, cooled to rt, diluted with diethyl ether (350 mL) and washed twice with 1 N aq. HCl and once with sat. aq. NaHCO3 solution. The organic extract is dried over MgSO4, filtered and evaporated. The residue is purified by flash chromatography on silica gel eluting with heptane:EA 19:1 to give 3-(2-ethyl-4-formyl-6-methyl-phenyl)-acrylic acid methyl ester (5.93 g) as a colourless liquid; LC-MS: tR=0.99 min. c) A suspension of 3-(2-ethyl-4-formyl-6-methyl-phenyl)-acrylic acid methyl ester (5.93 g, 25.53 mmol) in methanol (140 mL) and 2 N aq. NaOH (45 mL) is stirred at rt for 1 h. The methanol is evaporated and the aq. solution is extracted twice with DCM. The aq. layer is acidified with 37% aq. HCl. The precipitate that forms is collected, washed with water and dried. The product is further purified by recrystallisation from EA (100 mL) to give 3-(2-ethyl-4-formyl-6-methyl-phenyl)-acrylic acid (4.2 g) as yellow crystals; LC-MS: tR=0.87 min. d) To a solution of 3-(2-ethyl-4-formyl-6-methyl-phenyl)-acrylic acid (2.75 g, 12.6 mmol) and DIPEA (1.8 g, 13.8 mmol) in ethanol (80 mL), Pd/C (275 mg, 10% Pd, moistened with 50% water) is added. The mixture is stirred for 16 h at rt under 1 atm of H2. The catalyst is filtered off and the filtrate is concentrated. The residue is dissolved in EA, washed with 2 N aq. HCl, followed by 1 N aq. HCl and brine. The organic extract is dried over Na2SO4, filtered and evaporated to give 3-(2-ethyl-4-hydroxymethyl-6-methyl-phenyl)-propionic acid (2.8 g) as a white solid; LC-MS: tR=0.76 min. e) A solution of 3-(2-ethyl-4-hydroxymethyl-6-methyl-phenyl)-propionic acid (2.8 g, 12.6 mmol) in acetic acid (50 mL) is treated with MnO2 (3.9 g, 45.4 mmol) and the resulting mixture is stirred at 80° C. for 4 h. The mixture is filtered and the filtrate is concentrated. The crude product is purified by CC on silica gel eluting with DCM to give 3-(2-ethyl-4-formyl-6-methyl-phenyl)-propionic acid (1.76 g) as a beige solid; LC-MS: tR=0.86 min. f) A solution of 3-(2-ethyl-4-formyl-6-methyl-phenyl)-propionic acid (1.67 g, 7.58 mmol) and hydroxylamine hydrochloride (780 mg, 11.36 mmol) in 1-methyl-2-pyrrolidone is heated to 80° C. for 30 min in the microwave (300 W, active cooling during irradiation). The reaction mixture is diluted with diethyl ether and washed with water and brine. The organic extract is dried over Na2SO4, filtered and evaporated to give 3-(4-cyano-2-ethyl-6-methyl-phenyl)-propionic acid (1.55 g) as a beige solid; LC-MS: tR=0.89 min, 1H NMR (D6-DMSO): δ 12.25 (s, 1H), 7.45 (s, 2H), 2.91-2.84 (m, 2H), 2.67-2.59 (m, 2H), 2.35-2.30 (m, 5H), 1.14 (t, J=7.6 Hz, 3H). g) Potassium tert. butoxide (2.71 g, 24.1 mmol) is carefully dissolved in methanol (25 mL). To this solution hydroxylamine hydrochloride (1.44 g, 20.7 mmol) followed by 3-(4-cyano-2-ethyl-6-methyl-phenyl)-propionic acid (1.50 g, 6.90 mmol) dissolved in methanol (7.5 mL) is added. The mixture is refluxed for 8 h and the solvent is evaporated. The residue is dissolved in 2 N aq. HCl and extracted with EA. The pH of the aq. phase is adjusted to pH 5 by adding sat. aq. NaHCO3 and the mixture is extracted three times with EA. The combined organic extracts are dried over Na2SO4, filtered, evaporated and dried to give 3-[2-ethyl-4-(N-hydroxycarbamimidoyl)-6-methyl-phenyl]-propionic acid (1.4 g) as a white solid; LC-MS: tR=0.60 min, [M+1]+=251.17.

1. filtrationThe mixture is filtered
2. concentrationthe filtrate is concentrated
3. customThe crude product is purified by CC on silica gel eluting with DCM