Copper-catalyzed reaction of benzoxazinanones with sulfilimines: access to 2-ethynyl-benzoimidazoles via an abnormal skeletal rearrangement.

A copper-catalyzed reaction of benzoxazinanones with N -aryl sulfilimines has been developed, providing 2-ethynyl-benzoimidazoles in good to excellent yields (up to 98%) under mild reaction conditions. Importantly, the reaction proceeds via an abnormal skeletal rearrangement and annulation process, rather than an expected (4 + 1) annulation.