Reductive Deletion of Endocyclic Oxygen Atom in 1,2‐Oxazine N ‐Oxides to Access N ‐Hydroxypyrrolidines

Single‐atom ring‐editing strategies have emerged as a powerful tool for the diversification of molecular libraries through the remodeling of key heterocyclic scaffolds. The 1,2‐oxazine core represents an ideal platform for implementing single heteroatom deletion/swapping strategies, which lead to five‐membered O ‐ or N ‐heterocycles with varying levels of saturation. Here, we introduce a novel reductive ring contraction of 1,2‐oxazine N ‐oxides that achieves the formal deletion of the endocyclic oxygen atom, delivering synthetically valuable N ‐hydroxypyrrolidines. This process operates under mild reductive conditions with the NaBH ₃ CN/TsOH system via an unprecedented multistep ring opening/ring reconstruction sequence. The introduction of a recyclable chiral auxiliary enables a practical asymmetric variant, providing a route to enantioenriched N ‐hydroxypyrrolidines.