The photochemical isomerization in pyridazine-N-oxide derivatives

• Published in: Tetrahedron Vol. 164; p. 134173
• Main Authors: D'Auria, Maurizio, Emanuele, Lucia
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 10.09.2024
• Subjects: DFT calculations; Furan; Photoisomerization; Pyrazole; Pyridazine N-oxide; Furan; Photoisomerization; DFT calculations; Pyrazole; Pyridazine N-oxide
• ISSN: 0040-4020
• DOI: 10.1016/j.tet.2024.134173

DFT calculations on the photoisomerization reactions of pyridazine N-oxide derivatives are presented. The irradiation of 3,6-diphenylpyridazine N-oxide allowed to obtain the first excited singlet state that underwent to a ring opening reaction induced to the oxygen migration to the adjacent carbon atom, with the formation of a diazo derivative. This intermediate can give a ring closure reaction to give a pyrazole derivative, or, with a higher transition energy, it can lose nitrogen allowing the formation of 2,5-diphenylfuran. The irradiation of 3-phenylpyridazine N-oxide allowed the formation only of 2-phenylfuran. In this case, calculations allowed to explain this behavior. The first excited singlet state gave a photoisomerization reaction with the formation of the corresponding diazo intermediate. This intermediate could not be converted into the corresponding pyrazole derivative because it was converted into a N-formyl pyrazole never reported in literature. The only possible reaction is the loss of nitrogen and the formation of 2-phenylfuran. [Display omitted] •The first photochemical reactions of 3,6-diphenylpyridazine N-oxide is a ring opening reactions.•In the photoisomerization of 3,6-diphenylpyridazine N-oxide oxaziridine intermediates were not obtained.•The formation of furan derivatives occurs without any intermediate.•The selective formation of furan in 2-phenylpyridazine N-oxide derive from an unusual isomerization reaction.