CYCLOADDITIONS OF 1,5-AZULENEQUINONE AND 1,7-AZULENEQUINONE TO BENZO[C]FURAN AND ITS 1,3-DIPHENYL DERIVATIVE

With 1,3-diphenylbenzo[c]furan (DIBF), 1,5-azulenequinone (5-AQ) gave a [2+4] cycloadduct and a [2+4]-[6+4] cycloadduct which were interconv erted under mild conditions. This is the first observation of conjugat ed rearrangement of [2+4] mode to [6+4] mode with the second attack of cycloaddend or conjugated cycloreversion with the rearrangement. 1,7- Azulenequinone (7-AQ) formed two stereoisomeric 1:2-[2+4]-[6+4] cycloa dducts. With benzo[c]furan, 5-AQ and 7-AQ afforded two and four stereo isomeric [2+4]-[6+4] cycloadducts, respectively.