Cycloadditions of N-sulfonyl nitrones generated by lewis acid catalyzed rearrangement of oxaziridines

We have developed cycloaddition reactions of novel, electron-deficient N-nosyl nitrones that arise from the titanium(IV)-catalyzed rearrangement of the corresponding N-nosyl oxaziridines. A diverse range of styrenes and oxaziridines react smoothly in this transformation, producing structurally varied N-nosyl isoxazolidines in good yields and with excellent diastereoselectivity. Importantly, the nosyl protecting group can be easily removed under mild conditions without concomitant cleavage of the sensitive isoxazolidine nitrogen-oxygen bond, allowing efficient access to N-unsubstituted isoxazolidines for further synthetic manipulation and biological evaluation.