Stereochemical and Electronic Features of the [3 + 2] Cycloaddition of Pentafulvenes with Acylnitrones.

A series of mono- and di-substituted pentafulvenes 1–3 was reacted with aroylnitrones 4 to afford the corresponding fused bicyclic monoadducts 5–9, generally as a mixture of isomers. The stereochemistry of the addition reaction was established by 1D and 2D NMR spectroscopies or X-ray crystallography. Performance of theoretical calculations has been undertaken in order to rationalize the important differences in regioselectivity displayed by the reaction.