Copper‐Catalyzed Three‐Component Annulations of Alkenes, Nitrosoarenes, and N‐Hydroxyallylamines To Form Fused Oxazinane/Isoxazolidine Heterocycles

One‐pot cascade annulations among nitrosoarenes, alkenes, and N‐hydroxyallylamines have been achieved with CuCl/O 2 catalysts, forming fused oxazinane/isoxazolidine heterocycles with excellent diastereoselectivity (d.r. >20:1). To enhance the synthetic utility, we developed a successive cleavage of the two N−O bonds of the resulting heterocycles. A mechanism involving dipolar [3+2] cycloadditions of nitrone intermediates with their tethered alkenes is postulated for formation of these heterocycles.