Opening of the epoxide bridge in 3a,6-epoxyisoindol-1-ones by the action of BF3•Et2O 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 BF3 center dot Et2O in acetic anhydride at 25 degrees C over 1 h proceeds through an S(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-hexa-hydroisoindol-1-ones, which are aromatized under these conditions over 24 h to give 2,3-dihydro-1H-isoindol-1-ones.