Base‐Promoted Cycloaddition of γ‐Hydroxy‐ and δ‐Hydroxy‐α,β‐Unsaturated Carbonyls with Azaoxyallyl Cations: Rapid Synthesis of N,O‐Heterocycles

Metal‐free and environmentally friendly synthesis of morpholin‐3‐one and 1,4‐oxazepan‐3‐one skeletons was achieved by the cycloaddition reaction of alcohol‐tethered enones and α‐halohydroxamates. This transformation was proposed to proceed through the addition of the hydroxyl group in the enone to an in‐situ generated azaoxyallyl cation followed by intramolecular aza‐Michael‐type trapping. Accordingly, morpholin‐3‐ones and 1,4‐oxazepan‐3‐ones could be generated from γ‐hydroxy and δ‐hydroxy enones, respectively, in a highly diastereoselective manner. The synthesis of morpholin‐3‐one and 1,4‐oxazepan‐3‐one skeletons was achieved by the cycloaddition reaction of alcohol‐tethered enones and α‐halohydroxamates. This process proceeds through the addition of the hydroxyl group in the enone to an in‐situ generated azaoxyallyl cation followed by intramolecular aza‐Michael‐type trapping. Morpholin‐3‐ones and 1,4‐oxazepan‐3‐ones could be generated from γ‐hydroxy and δ‐hydroxy enones, respectively.