MEDIUM-SIZED CYCLOPHANES - BROMINATION OF 8-METHOXY[2.2]METACYCLOPHANES

When 8-methoxy[2.2]metacyclophanes 5 are treated with benzyl trimethylammonium tribromide in dichloromethane, the transannular reaction products, tetrahydropyrene 6 and 7 are obtained along with 5-bromo-8-methoxy[2.2]metacyclophanes 8. The bromination of 5-tert-butyl-8-methoxy[2.2]metacyclophanes 9a-9g in dichloromethane is carried out under the same conditions to afford tetrahydropyrene derivatives exclusively. On the other hand, when the bromination reactions are performed in various alcohols, alkoxy-substituted tetrahydropyrenes 11 and 12 are obtained in good yields, which are easily dehydrogenated with DDQ to afford the corresponding pyrene derivatives. The reaction mechanisms of the above reactions are also discussed.