Reactivity of (Z)-4-arylidene-5(4H)-oxazolones: [4+2] cycloaddition versus [4+3] cycloaddition/nucleophilic trapping

The use of different aluminum derivatives in the reaction between cyclopentadiene and (Z)-2-phenyl-4-arylidene-5(4H)-oxazolones, and in particular the use of different equivalents of the reagent, allows the modulation of the synthesis of the norbornane skeleton by a [4+2] cycloaddition or the more interesting bicyclo[3.2.1]octane framework by a [4+3] cycloaddition followed by nucleophilic trapping of the ionic dipole cycloadduct with cyclopentadiene.