Catalyst-free photooxidation reaction from 1,4-dihydropyridazine to pyridazine under air

In the inverse electron-demand Diels-Alder (iEDDA) reactions between tetrazines and strained alkenes, a mixture of 1,4-dihydropyridazine isomers are formed first, and they are then oxidized to pyridazines. Although the products of these related oxidation processes converge as pyridazines, the oxidation rate is quite low with some substrates. In this study, we revealed that 1,4-dihydropyridazines formed in the iEDDA reactions were oxidized to pyridazines by simply irradiating with an ultraviolet light under an air atmosphere. Our experimental results implied that singlet oxygen was formed in the course of the re-actions to oxidize the 1,4-dihydropyridazine molecules. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In the inverse electron-demand Diels-Alder reactions, a mixture of 1,4-dihydropyridazine isomers is formed first and then oxidized to pyridazines. This study revealed that 1,4-dihydropyridazines formed in the reactions can be oxidized to pyridazines simply by irradiating with ultraviolet light under an air atmosphere. Experimental results suggest that singlet oxygen plays a key role in oxidizing the 1,4-dihydropyridazine molecules.