Potassium Permanganate → 5-Methoxy-4-(4-methoxy-4-oxobutoxy)-2-nitrobenzoic acid

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The slightly wet nitroaldehyde 12 (80 g, wet) was dissolved in acetone (500 mL) in a 2 L flask fitted with a condenser and a mechanical stirrer. A hot solution of 10% potassium permanganate (50 g in 500 mL of water) was quickly added via a dropping funnel (in 5 to 10 minutes). Halfway through the addition the solution began to reflux violently and until the end of the addition. The solution was allowed to stir and cool down for an hour and was then filtered through celite and the brown residue was washed with 1 L of hot water. The filtrate was transferred in a large flask and a solution of sodium bisulfite (80 g in 500 mL 1N HCl) was added. The final volume was adjusted to 3 L by addition of water, and the pH was adjusted to 1 with conc. HCl. The product 42 precipitated and it was filtered and dried. 31 g (50% yield over 2 steps). The product was pure as proved by TLC (85/15/0.5 EtOAc/MeOH/Acetic acid). 1H NMR (CDCl3) δ 7.33 (1H, s), 7.19 (1H, s), 4.09 (2H, t, J=5.72 Hz), 3.91 (3H, s), 3.64 (3H, s), 2.50 (2H, t, J=6.98 Hz), 2.14 (2H, p, J=6.33 Hz); 13C NMR (DMSO-d6) δ 172.8, 166.0, 151.8, 149.1, 141.3, 121.2, 111.3, 107.8, 68.1, 56.4, 51.3, 29.7, 23.8; IR (golden gate) vmax 1736, 1701, 1602, 1535, 1415, 1275, 1220, 1054, 936, 879, 820, 655 cm−1; MS (ES−) m/z (relative intensity) 312.01 ([M−H]−, 100).

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