Opening of the epoxide bridge in 3a,6-epoxyisoindol-1-ones by the action of B[F.sub.3] x [Et.sub.2]O in acetic anhydride

The opening of the epoxide bridge in N-substituted 2,3,7,7a-tetrahydro-3a,6- epoxyisoindol-1-ones by the action of B[F.sub.3] x [Et.sub.2]O in acetic anhydride at 25°C over 1 h proceeds through an [S.sub.N]1 mechanism. The allylic type cation formed in the first step is stabilized by the addition of an acetoxy group at C-5 in the isoindole system to give a mixture of cis and trans isomers of 5,6-diacetoxy- 2,3,5,6,7,7a-hexahydroisoindol-1-ones, which are aromatized under these conditions over 24 h to give 2,3-dihydro1H- isoindol-1-ones. Keywords: 3a,6-epoxyisoindole, furan, furfurylamine, isoindole, 7- oxabicyclo[2.2.1]heptene, aromatization, intramolecular Diels-Alder reaction.