Benzonitrile Oxide Cycloadditions with Exocyclic Methylene Benzothiazepine Dioxides

N-substituted 5-methylene-2,3,4,5-tetrahydrobenzo[f][1,2]thiazepine 1,1-dioxides underwent 1,3-dipolar cycloaddition with benzonitrile oxide, generated in situ, to give isoxazoline spiro adducts. The cycloadditions were completely regioselective to give the hitherto unreported 3,4-dihydro-2H,4′H-spiro[benzo[f][1,2]thiazepine-5,5′-isoxazole] 1,1-dioxide cycloadduct. Where the N-substituent on the sulfonamide cycloaddition precursor was a 2-substituted arene, the resulting atropisomerism along the N-aryl bond led to facial selectivity in the cycloaddition reaction, with greater than 90 % diastereoselectivity.