Gold‐Catalyzed Synthesis of Tetrahydropyrrolo Oxazine Derivatives From the Reactions of <i>Ortho</i> ‐Substituted 2‐Alkenyl‐1‐arylalkynes and Nitrones

Catalytic bicyclic annulations between ortho ‐substituted 2‐alkenyl‐1‐arylalkynes and nitrones to afford tetrahydropyrrolo[2,3‐ d ][1,2]oxazines are described. This work demonstrates a steric effect of ortho ‐substituents of 2‐alkenyl‐1‐arylalkynes to alter the reaction chemoselectivity. With control experiments, we postulate a mechanism involving an initial attack of N ‐hydroxyaniline at gold‐π‐alkyne intermediates, resulting in a key intermediate, which permits only a 1,2‐proton transfer instead of an intermolecular deprotonation, due to the steric effect.