In the presence of a more powerful base/nucleophile or at higher temperatures a different mechanism for NAS can occur. While studying NAS reactions, researcher encountered some unexpected regichemistry.
When they labeled the carbon attached to the Cl atom with a 13C they observed the following two products in equal amounts.
They proposed the following elimiation/addition sequence and proved it by traping the benzyne intermediate.
The benzyne intermediate was trapped with 1,3-butadiene via a Diels-Alder reaction. See if you can predict the Diels Alder product.