Efficient asymmetric selenocyclizations of alkenyl oximes into cyclic nitrones and 1,2-oxazines promoted by sulfur containing diselenides

Treatment of the di-2-(1S)-1-(methylthio)ethyl]phenyl diselenide or of the di-2-methoxy-6-(1S)-1-methylthio)ethyl]phenyl diselenide with bromine and silver triflate afforded the corresponding electrophilic selenylating triflates which were used in situ to promote the asymmetric selenocyclization of γ-alkenyl oximes and δ-phenyl-γ-alkenyl oximes. The course of these reactions and hence the structures of the cyclization products were dictated by the (E)- or (Z)-geometry of the starting oximes. The two types of cyclization products were either the cyclic nitrones or the 1,2-oxazines; in both cases the reactions proceeded with excellent yields, complete regioselectivity and good diastereoselectivity.