Product and mechanistic studies of the anodic oxidation of methoxylated naphthalenes. The EECrCp mechanism

Article abstract of DOI:10.1021/ja00399a037

The anodic oxidations of 1- and 2-methoxy- and 1,2-, 1,3-, 1,4-, 1,5-, 1,6-, 1,7-, 2,3-, 2,6-, and 2,7-dimethoxynaphthalenes have been studied in methanolic potassium hydroxide. At lower temperatures (0-20°C) the major process in 1-methoxynaphthalene and 1,5-, 1,6-, and 1,7-dimethoxynaphthalenes is two-electron oxidation resulting in addition of methoxy groups across the 1,4-positions followed by loss of methanol on workup to afford the methoxylated naphthalene. In contrast, 2-methoxynaphthalene and 1,3-, 2,3-, 2,6-, and 2,7-dimethoxynaphthalenes give major amounts of products derived from four-electron oxidation under these conditions. When the anodic oxidation of this first class of compounds was conducted in refluxing methanol, increased amounts of four-electron oxidation products were isolated. While 1-methylnaphthalene and naphthalene also undergo anodic oxidation under these conditions, these unactivated systems react less selectively and efficiently. Mechanistic studies are most consistent with the key step of the anodic oxidation under these conditions being the reaction of methoxy radical with the aromatic radical cation. This reaction sequence is termed the EEC_rC_p mechanism, and the results of the oxidation of the methoxylated naphthalenes above are discussed in this format.