Facial selectivity induced by N-aryl atropisomerism in benzonitrile oxide cycloadditions with 4-methylene-2-oxazolidinones

N-Aryl 4-methylene-2-oxazolidinones, prepared via the corresponding O-propargyl carbamates, underwent nitrile oxide cycloaddition with benzonitrile oxide to give 5-spiro isoxazoline adducts with complete regioselectivity. Steric hindrance by atropisomerism around the N-aryl bond induced facial selectivity in these cycloadditions.