[C:1]([O:5][C:6]1[CH:13]=[CH:12][C:9]([CH:10]=[O:11])=[CH:8][C:7]=1[O:14][CH3:15])([CH3:4])([CH3:3])[CH3:2].[OH-].[K+].[O-:18][Mn](=O)(=O)=O.[K+]>O1CCOCC1>[C:1]([O:5][C:6]1[CH:13]=[CH:12][C:9]([C:10]([OH:18])=[O:11])=[CH:8][C:7]=1[O:14][CH3:15])([CH3:4])([CH3:3])[CH3:2]4-tert-Butoxy-3-methoxybenzaldehyde (130 mg, 0.62 mmol) was suspended in a mixture of dioxane (520 μL) and potassium hydroxide (6.5 mL of 0.20 M, 1.3 mmol). KMnO4 (150 mg, 0.93 mmol) was added and the reaction was stirred vigorously for 16 h. The reaction mixture was filtered and then concentrated to 3 mL. Hydrochloric acid (1M, 4 mL) was added and the resulting precipitate was filtered (after standing for 15 minutes) and washed with 1M HCl and a small amount of water to yield 4-tert-butoxy-3-methoxy-benzoic acid (68 mg, 49%) as a white solid. Rf=0.23 (SiO2, 40% ethyl acetate in hexanes); ESI-MS m/z calc. 224.1. found 225.2 (M+1)+. Retention time: 1.66 minutes (3 min run). 1H NMR (400 MHz, DMSO) δ 12.80 (s, 1H), 7.66-7.41 (m, 2H), 7.09 (d, J=8.8 Hz, 1H), 3.78 (s, 3H), 1.32 (s, 9H). The following compounds were synthesized using the procedures described above: 4-tert-butoxy-3-methylbenzoic acid from 4-hydroxy-3-methylbenzaldehyde, 2-fluoro-4,5-dimethoxybenzoic acid from 2-fluoro-4,5-dimethoxybenzaldehyde, 4-tert-butoxy-2-methoxybenzoic acid from 4-hydroxy-2-methoxybenzaldehyde, 4-tert-butoxy-2-fluorobenzoic acid from 2-fluoro-4-hydroxybenzaldehyde, and 4-tert-butoxybenzoic acid from 4-hydroxybenzaldehyde.
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