N‐Protected 1,2‐Oxazetidines as a Source of Electrophilic Oxygen: Straightforward Access to Benzomorpholines and Related Heterocycles by Using a Reactive Tether

Abstract A hitherto unknown reactivity of a strained four‐membered heterocycle, 1,2‐oxazetidine, is reported. When reacted with organometallic compounds, this reagent provides electrophilic oxygen with a nitrogen‐terminated two‐carbon‐atom tether. The synthetic versatility of the products obtained was demonstrated in various transformations, leading to efficient synthesis of six‐, seven‐, and eight‐membered heterocyclic systems of pharmaceutical importance.