Temperature- and substituent-dependence in the photosensitized oxygenation of N,N-disubstituted hydrazones

Methylene blue-sensitized photooxidation of N,N-disubstituted hydrazones 1a-f gave various products 2-9, depending on the reaction temperature and N-substituents. The major reaction modes from the photo-oxidation of N,N-diphenylhydrazones were α-oxidation at room temperature and C=N cleavage at −78 °C in contrast to C=N cleavage as an only reaction mode for the photooxidation of N,N-dimethylhydrazones at either room temperature or −78 °C.