反应详情

At -10° C., AlCl3 (2.437 g, 18.3 mmol) was added to a solution of the styrene of Step 7 (1.013 g, 2.28 mmol) and 3-mercapto-2-methylpropanoic acid (356 mg, 2.96 mmol, obtained from the hydrolysis of ethyl 3-mercapto-2-methylpropanoate (Example 1, Method B, Step 6) as in Example 7, Step 4, or alternatively from the NaOH hydrolysis of ethyl 3-(acetylthio)-2-methylpropanoate) in 25 mL of CH2Cl2 and the mixture was stirred at 0° C. in the dark for 2 h. Cold aq NH4OAc, EtOAc and THF were then added and the mixture was stirred until complete dissolution of the oil. The product was extracted with EtOAc:THF 1:1, dried over Na2SO4 and concentrated. The sodium salt of the acid was formed in EtOH with 500 μl of 10N NaOH. It was purified on an Amberlite ion exchange resin XAD-8: elution with water separate the sodium 3-mercapto-2-methyl-propanoate and elution with methanol afforded the title acid as an impure sodium salt. The compound was dissolved in saturated aq NH4Cl, extracted with EtOAc:THF 1:1, dried over Na2SO4 and purified by flash chromatography on silica using acetone:toluene:acetic acid 5:95:1 to yield 766 mg (60%) of the title acid.