Regioselective transformation of O-propargylic arylaldoximes to four-membered cyclic nitrones by copper-catalyzed skeletal rearrangement.

(E)-O-Propargylic arylaldoximes were regioselectively converted, in the presence of copper catalysts, into their corresponding four-membered cyclic nitrones in good to excellent yields. The reactions proceeded via a tandem [2,3]-rearrangement and 4π-electrocyclization of the N-allenylnitrone intermediate and involved cleavage of the carbon-oxygen bond.