Methanol → 3,5-Bis-acetylamino-2-bromo-benzoic acid methyl ester

Participants

Reaction Conditions

Reaction Steps

To acetic acid (250 mL) at room temperature was added Intermediate 6(a) (15.49 g, 50.79 mmol). The mixture was placed in an oil bath at 40° C. for c.a. 10 min and stirred vigorously under an Ar atmosphere until the solution went clear. Iron powder (25.34 g, 453.72 mmol) was added and the mixture was heated at 40° C. for c.a. 6 hours. The mixture was filtered through diatomaceous earth, rinsing with methanol. The combined filtrate and rinses were evaporated to give orange solids, which were determined to be a mixture of products (13.2 g) resulting from incomplete reduction of the nitro groups. This mixture (13.1 g) in CH2Cl2 (48 mL) and N,N-dimethylformamide (5 mL) was then treated with acetic anhydride (36 mL, 382 mmol) and stirred overnight under an Ar atmosphere. The CH2Cl2 was evaporated and the mixture was partitioned between ethyl acetate and saturated aqueous NaHCO3. The aqueous layer was extracted twice with ethyl acetate and the combined extracts were washed successively with 1:1 H2O:saturated aqueous NaHCO3 (multiple washings), 0.5 M aqueous HCl (X2), saturated aqueous NaHCO3 (X2) and brine. The ethyl acetate solution was then dried (Na2SO4), filtered and evaporated to give yellow solids, which were then triturated with diethyl ether (c.a. 75 mL) to give a mixture of acetylated products (11.4 g) as a yellow solids. A portion of this mixture of acetylated products (5.5 g) in acetic acid (17.4 mL) was then treated with acetic anhydride (16.5 mL, 174 mmol) and iron powder (9.74 g, 174 mmol) and heated at 40° C. under an Ar atmosphere overnight. Methanol was then added and the reaction was stirred at room temperature for c.a. 1.5 hours. Then 9:1 CH2Cl2:methanol was added, and the mixture was filtered through diatomaceous earth, rinsing with 9:1 CH2Cl2:methanol. The combined filtrate and rinses were evaporated and again methanol was added and the mixture was stirred c.a. 0.5 hours after which the methanol was evaporated. Ethyl acetate was added followed by hexane to precipitate orange solids (6.9 g) which were collected. Silica gel chromatography eluting with 1:1 acetone:hexane which afforded, after isolation, Intermediate 6(b) (4.1 g, 12.46 mmol) as a cream solid in 49% yield.

Provenance & Evidence