反应详情

Methyl 4,5-dimethoxy-2-nitrobenzoate (4.8 g, 20 mmol) was hydrolyzed to the corresponding carboxylic acid by refluxing overnight with KOH (1.6 g, 40 mmol) in 1:1 methanol/benzene (100 mL). The mixture was concentrated to give the crude carboxylate, dissolved in H2O, and precipitated as 4,5-dimethoxy-2-nitrobenzoic acid with 2N HCl. This acid (2.27 g, 10 mmol) was then converted to the corresponding acid chloride by refluxing in benzene (30 mL) with thionyl chloride (1.66 g, 14 mmol) for 1 hour. The crude mixture was concentrated in vacuo and diluted with dichloromethane (10 mL). This solution was added to a cooled solution of (3S,4R)-4-amino-2,2-dimethyl-6-(trifluoromethoxy)-chroman-3-ol (2.75 g, 10 mmol), triethylamine (1.39 mL, 10 mmol) and dichloromethane (25 mL). The crude benzamide was worked-up in a method similar to that in Example 1 and chromatographed (1:1 hexanes/ethyl acetate) to afford 2.74 g (56%) of white solid: m.p. 97°-100°0 C.; 1H NMR (DMSO-d6): δ 9.00 (s, 1H), 7.62 (s, 1H), 7.39 (d, 1H), 7.25 (s, 1H), 7.16 (d, 1H), 6.86 (d, 1H), 5.86 (d, 1H), 4.96 (br t, 1H), 3.91 (s, 3H), 3.89 (s, 3H), 3.64 (dd, 1H), 1.43 (s, 3H), 1.20 (s, 3H).

1. concentrationThe mixture was concentrated
2. customto give the crude carboxylate
3. customprecipitated as 4,5-dimethoxy-2-nitrobenzoic acid with 2N HCl
4. concentrationThe crude mixture was concentrated in vacuo
5. additiondiluted with dichloromethane (10 mL)
6. customchromatographed (1:1 hexanes/ethyl acetate)