Photochemistry of pyrimidin-2(1H)-ones: intramolecular γ-hydrogen abstraction by the nitrogen of the imino group
Abstract
Irradiation of 1-aryl-4-propyl -(1a) and 1-aryl-4-(3-ethoxypropyl)-6-methylpyrimidin-2(1H)-ones (1b–d) gave the photoelimination products, 1-aryl-4,6-dimethylpyrimidin-2(1H)-ones (2a–d), via intramolecular γ-hydrogen atom abstraction of the excited imino nitrogen of the starting pyrimidin-2(1H)-one (1), in addition to the 1,3-diazabicyclo[2.2.0]hex-5-en-2-ones (3a–d). The pyrimidin-2(1H)-ones (1f) and (1h), which have no γ-hydrogens at the C-4 position, underwent photochemical electrocyclization to give the 1,3-diazabicyclo[2.2.0]hex-5-en-2-ones (3f) and (3h) as the sole products.