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.