INTRAMOLECULAR ANODIC CARBON-CARBON BOND FORMATION FROM OXIDIZED PHENOL INTERMEDIATES - EFFECT OF OXYGENATED SUBSTITUENTS ON THE YIELDS OF SPIRO DIENONES IN ELECTROCHEMICAL AND IODOBENZENE DIACETATE OXIDATIONS

The single-cell, constant-current anodic oxidation of a series of 4-(2 -alkenylaryl)phenols was studied in which the aryl substituents were 2 -vinyl-4,5-dimethoxy, 6a; 2-propenyl-4,5-dimethoxy, 9a; 2-vinyl-4,5-me thylenedioxy, 6b; 2-propenyl-4,5-methylenedioxy, 9b; 2-vinyl-4-methoxy , 6c; 2-propenyl-4-methoxy, 9c; 2-vinyl-5-methoxy, 6d; and 2-propenyl- 5-methoxy, 9d. Two compounds having methoxyl groups on the phenolic ri ng were also studied: 4-(2'-propenylphenyl)-2-methoxyphenol, 9e, and 4 -(2'-propenylphenyl)-3-methoxyphenol, 9f. A novel synthetic route to t he methoxy compounds 6c, 9c, 6d, and 9d was developed. This involved a s a key step the MAD, 2,6-ditert-butyl-4-methylphenoxide)methylaluminu m, mediated addition of organolithium and Grignard reagents to functio nalize quinol ether derivatives. Anodic oxidation of compounds 6a, 9a, 9b, 6c, 9c, and 9d gave good yields of spiro dienones arising from tr apping of the phenoxonium ion by the alkenyl side chain followed by re action of the resulting cation with methanol. The products from the el ectrochemical oxidation of these 4-(2'-alkenylaryl)phenols were compar ed with those obtained from the iodobenzene diacetate oxidations. In g eneral, the compounds that gave good yields of spiro dienones from ele ctrochemical oxidation gave good yields from iodobenzene diacetate oxi dations. However, there were two cases in which the results of the two oxidations did not parallel each other. Whereas anodic oxidation of 9 f gave a low yield of spiro dienone, the iodobenzene diacetate route g ave a 74% yield of this product. In the case of 9d, the opposite effec t was noted: the electrochemical route gave a higher yield than did th e iodobenzene diacetate oxidation.