A suspension of 2-(5-oxo-10,11-dihydrodibenzo[a,d]cyclohepten-2-yl)propionamide (15 g,53.7 mmol) in a mixture of sulphuric acid (d = 1.36, 50 mL) and water (60 mL) was heated with vigorous stirring for 3 hours at 110°C. After cooling, the product which precipitated was filtered off and then added to 2 N sodium hydroxide solution (55 mL). The alkaline solution, clarified by filtration, was acidified by adding 2 N hydrochloric acid (60 mL). The product which precipitated was filtered off, dried and then recrystallized from CCl4 (170 mL) to give 2-(5-oxo-10,11-dihydrodibenzo[a,d]cyclohepten2-yl)propionic acid (7.4 g, 49.2%) melting at 122°C.
A solution of 4-(1,1-diphenylpropyl)-picolinamide (3.8 g, 0.012 mol) in ethanol (50 mL) was added 10% aqueous potassium hydroxide (100 mL) and the resulting mixture was heated at reflux overnight。The solvent was removed under reduced pressure and the residue was added water then adjusted to about pH 5 with 10% aqueous hydrochloric acid. The resulting solid was filtered and recrystallized from ethanol to obtain the desired compound of this example (1.6 g, 42.0%) melting at 191~193°C.
To a solution of 4-carbamoyl-3-methoxyisothiazole (7.9 g, 0.05 mole) in 90 mL of 80% sulfuric acid at 10~15°C was added slowly beneath the surface of the liquid a solution of sodium nitrite (9.5 g, 0.137 mol) in water (13 mL). When the addition was complete the solution was allowed to come to 25°C and then was heated to 60°C for several minutes. After cooling to 25°C the reaction solution was poured onto ice to afford 4-carboxy-3-methoxyisothiazole (3.64 g, 46%) as a white solid melting at 182~185°C.
To a 0.5 M solution of (R)-N-Methyl-3-phenylbutanamide (194 mg, 1.09 mmol) in methylene chloride was added triethylamine (0.15 ml, 1.09mmol), di-tert-butyl dicarbonate (0.5 ml, 2.18 mmol) and 4-(dimethylamino)pyridine (150 mg, 1.11 mmol). The solution was stirred for 8 h at room temperature. The volatiles were removed and the residue was purified by flash chromatogramphy (1/20 (v/v) EtOAc/hexane) to afford the desired (R)-N-Boc-N-Methyl-3-phenylbutanamide (210 mg, 70%).
A 0.2 M solution of (R)-N-Boc-N-Methyl-3-phenylbutanamide (175 mg, 0.63 mmol) in THF (4 ml), under N2 atmosphere, was cooled to 0°C. To this solution was added 1 N lithium hydroxide (2.0 ml, 2.0 mmol). The reaction mixture was allowed to stir for 6 h. After removal of THF in vacuo, the basic residue was acidified with 5% HCl and extracted with ether (3 ×15 ml). The combined ether layers were dried over anhydrous MgSO4, filtered and concentrated under reduced pressure. The residue was purified by bulb-to-bulb distillation
(110~120°C/1.2 mmHg) to give the desired (R)-3-phenylbutyric acid (85 mg, 85%).
【J. Org. Chem., 1996, 61, 4542-4554】