Photochemical and Thermal Reactions of Aromatic Schiff Bases

Article abstract of DOI:10.1021/jo00334a029

The photochemical and thermal reactions of aromatic Schiff bases (SB) prepared from o-aminophenol and aldehydes and from o-aminophenol and ketones are compared.All SB's are converted by light into the corresponding benzoxazolines.For the SB's derived from aldehydes, benzoxazoline formation is a prerequisite to convert them by a second photon into benzoxazoles.In some cases oxygen is not required for this second reaction step.SB's derived from ketones are converted into benzoxazoles by the absorption of just one photon, but only in the presence of oxygen and only if the aliphatic residue R₁ of the N=C(R₁R₂) bridge contains at least two carbon atoms.A radical mechanism is proposed for this reaction.Benzoxazine formation is observed in some cases as a thermal side reaction.The photochemical reactions of the latter were also investigated.