Singlet oxygen pyridones

In contrast to some analogous structures, pyrido[2,l-f][l,2,4]triazine 108 is quite stable toward atmospheric oxygen. It reacts, however, with singlet oxygen in a cycloaddition reaction, and the intermediate 109 thus formed loses nitrogen resulting in the pyridone 110 (Scheme 8) <2001JHC205>. 

Matsumoto, M Nasu, S., Takeda, M., Murakami, H. and Watanabe, N. (2000) Singlet oxygenation of 4-(4-tert-butyl-3,3-dimethyl-2,3-dihydrofuran-5-yl)-2-pyridone non-stereospecific 1,4-addition of singlet oxygen to a 1,3-diene system and thermal rearrangement of the resulting 1,4- endoperoxides to stable... 

Pyranones undergo DielsAlder reactions with maleic anhydride adducts of type 408 are formed which can lose carbon dioxide and react with more anhydride to give 409. 2-Pyranones also react with singlet oxygen to give endoperoxides 410. Benzyne reacts with l-methyl-2-pyridone to give 411. 

N-Substituted pyridone 233 reacts with singlet oxygen to form the endoperoxide 234 (Equation 67) <2005CC483>. 

Fluridone is a herbicide that is a gamma-pyridone derivative. It is a carotenoid inhibitor this is a well-known type of activity that interferes with the photosynthesis process in such a way as to lead to production of the plant-lethal singlet oxygen. 

The addition of singlet oxygen to 2-pyridones leads to oxygenated products derived from intermediates 163 (Scheme 16). All reported examples carry alkyl substitution of the pyridone at C3 (164) or C6 (26). Acidic hydrolysis (methanolysis) of these intermediates yield dicarbonyl products 165 and 166. ... 

Both products arise from the singlet state of the pyridone since the reaction could not be quenched by oxygen or hexa-2,4-dienol. Similar behaviour was observed for 5-chloropyridone in ethanol. However, 3- and 4-chloropyridone only yield the [4 + 4] dimers on irradiation in methanol or ethanol. It appears that concentration is the factor which controls whether dimerization or valence bond isomerization occurs. 

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