Synthesis of 1,2,5‐Oxadiazinane Derivatives by Photochemical Cycloaddition of Nitrones with Diaminomethanes

1,2,5‐Oxadiazinanes have a unique heterocyclic skeleton and are expected to be applicable to the synthesis of drugs. However, there have been few reported methodologies to synthesize these structures. We report a facile synthesis of 1,2,5‐oxadiazinanes that is accomplished by the unprecedented photochemical cycloaddition reaction of nitrones with diaminomethanes. The photoreaction is a formal [3+3] cycloaddition, where a nitrone and a diaminomethane act as the 1,3‐dipole and the 1,3‐synthon, respectively. The reaction is significantly accelerated with benzophenone as a photosensitizer. A high degree of diastereoselective addition (d.r. >99 : 1) is observed in the reaction of (Z)‐N‐benzyl‐1‐phenylmethanimine oxide with di(pyrrolidin‐1‐yl)methane. Novel [3+3] Reaction: A facile synthesis of 1,2,5‐oxadiazinanes is accomplished by a photochemical cycloaddition reaction of nitrones with diaminomethanes. Diaminomethanes are converted into the α‐aminoalkyl radical in a regioselective manner by hydrogen ion and serve as the 1,3‐synthon which reacts with nitrones as the 1,3‐dipole. The reaction is significantly accelerated when benzophenone was used as a photosensitizer. A high degree of diastereoselective addition (d.r. >99 : 1) is observed.