Directed, DDQ-promoted benzylic oxygenations of tetrahydronaphthalenes

Positional preferences for-para benzylic oxygenation of tetrahydronaphthalenes by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-aqueous dioxane were investigated by comparing the tetralone products from 6-hydroxy-7-methoxy- and 6-acetoxy-7-methoxy-1,2,3,4-tetrahydronaphthalene. The directing influence by an aromatic substituent on para benzylic oxygenation was in the order OH > OMe > OAc. Consistent with this finding were results obtained from lignan analogues. Treatment of (+)-beta-conidendryl alcohol with DDQ in dry dioxane resulted in the intramolecular bridging by one of two primary hydroxy groups to the benzylic position, giving an oxabicyclo[3.2.1]octane. Similar treatment of (+)-dimethyl-beta-conidendryl alcohol resulted in bridging by the alternate primary hydroxyl group to the benzhydrylic carbon giving an isomeric oxabicyclo[3.2.1]octane.