Facile Formation of o- and p-Tropoquinone Mono- and Bisacetals by Anodic Oxidation of 2,3-, 2,5-, 2,7-, and 4,5-Dimethoxytropones

Article abstract of DOI:10.1246/bcsj.61.3965

o- and p-Tropoquinone mono- and bisacetals (tetramethoxycycloheptadienones) were prepared from 2,3-, 2,5-, 2,7-, and 4,5-dimethoxytropones by means of anodic oxidations in practical yields.Cerium(IV) salt oxidations of dimethoxytropones afforded a mixture of products i.e., a hydrolysis product and/or a methanol adduct of tropoquinone bisacetals.By treating with sulfuric acid in a mixture of acetic acid and acetic anhydride, 4,4,7,7- and 2,2,7,7-tetramethoxycycloheptadienones gave the Thiele-type reaction products with a high positional selectivity.Similarly, 2-bromo-7-methoxytropone was anodically oxidized to 4,4,7,7-tetramethoxycycloheptadienone and its 2-bromo derivative.The mechanism of the reaction is also discussed in detail.