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Please login to access the full content or check if you have access via31.5.1.1.3 Method 3: Substitution of Hydrogen via Electrochemical Hydroxylation Using Electron-Withdrawing Groups
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González-Bello, C.; Castedo, L., Science of Synthesis, (2007) 31, 280.
Direct monohydroxylation of benzenes substituted with electron-withdrawing groups can be efficiently achieved by electrochemical oxidation. The reaction is usually performed in a mixed trifluoroacetic acid/dichloromethane solvent, in the presence of excess triethylamine, and using a divided cell equipped with a platinum anode and a carbon rod cathode.[48] After aqueous workup, good yields of the corresponding monophenols are obtained. It has been shown that the reaction proceeds via the formation of an aromatic trifluoroacetoxy cation that is oxidized and then hydrolyzed to afford the corresponding phenol. Monosubstituted benzenes 5 give a mixture of all three positional phenol isomers 6 (Scheme 5).[48] However, disubstituted benzenes 7 afford mainly the para oxidation products 8, with some of the ortho-isomer 9 (Scheme 6).[48]
Meeeee 8 Meeeeeeeeeeeeee Meeeeeeeeeeee ee Meeeeeeeeeeeeee Meeeeeee[88]
| M8 | Meeee (e/e/e) | Meeeee (%) | Mee |
|---|---|---|---|
| M | – | 88 | [88] |
| Me | 88:8:88 | 88 | [88] |
| Me | 88:8:88 | 88 | [88] |
| M | 88:8:88 | 88 | [88] |
| MM8 | 88:88:88 | 88 | [88] |
| MMMe | 88:88:88 | 88 | [88] |
| MM8Me | 88:88:88 | 88 | [88] |
| MMM | 88:88:88 | 88 | [88] |
| MM | 88:88:88 | 88 | [88] |
| MM8 | 88:88:88 | 88 | [88] |
e Meeeee eee eeeeee eeeeeeeeee ee MM.
Meeeee 8 Meeeeeeeeeeeeee Meeeeeeeeeeee ee Meeeeeeeeeeee Meeeeeee[88]
| M8 | M8 | M8 | Meeee (%) ee 8 | Meeee (%) ee 8 | Mee |
|---|---|---|---|---|---|
| Me | Me | M | 88 | 88 | [88] |
| Me | Me | M | 88 | 88 | [88] |
| M | M | M | eeeee | 8 | [88] |
| Me | M | Me | 88 | 8 | [88] |
| M | M | M | 88 | 88 | [88] |
References
| [48] | Meeeeeee, M.; Meeeee, M.; Meeeeee, M.; Meeeeeeee, M.; Meeeee, M.; Meeeeeeeee, M., Meeeeeeeeee, (8888) 88, 8888. |
Meeeeee Meeeeeeeeee
- 8.Meeeee-Meee, (8888) 8/8e8, 88.
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