Synthesis of 1,2‐ <i>N/O</i> ‐Heterocycles via Metal Hydride Hydrogen Atom Transfer Radical Cyclization on Vinylogous <i>N</i> ‐Alkoxycarbamates

Metal hydride hydrogen atom transfer‐mediated intramolecular cascade radical cyclization of vinylogous N ‐alkoxycarbamate is described for the stereoselective synthesis of 1,2‐oxazinane and 1,2‐oxazepane derivatives. This strategy relies on 6‐ exo‐trig and 7‐ exo‐trig radical cyclizations of alkenyl vinylogous N ‐alkoxycarbamate. The influence of nitrogen protecting groups on the efficiency and outcome of the radical cyclization was systematically investigated. Furthermore, the developed methodology enables the construction of structurally unique oxa‐aza ‐spirocyclic frameworks, expanding the synthetic utility of this radical cascade approach.