Methyl acetoacetate was irradiated in the presence of cyclohexene to afford methyl 3-cyclohexyl-3-hydroxybutyrate (VIII), methyl 3-cyclohexenyl-3-hydroxybutyrate (IX), two oxetanes (Xa and Xb), and cyclohexene dimers. In contrast to acetylacetone, acetoacetate behaves as a saturated ketone rather than as an α,β-unsaturated ester on photoreaction. We concluded that the n-π* excitation of the enol-form of β-dicarbonyl compound is responsible for photo-cycloaddition, and no effective n–π* excitation is accesisble on irradiaron of the enol-form of acetoacetate, since the enol form of acetoacetate has its n–π* and π-π* absorptions in the same region.
在
环己烯存在下辐照
乙酰乙酸甲酯,可得到
3-环己基-3-羟基丁酸甲酯 (VIII)、3-
环己烯基-
3-羟基丁酸甲酯 (IX)、两种氧杂
环丁烷 (Xa 和 Xb) 以及
环己烯二聚物。与
乙酰丙酮不同,
乙酰乙酸酯在光反应中表现为饱和酮,而不是 α、β-不饱和酯。我们得出的结论是,β-二羰基化合物烯醇形式的 n-π* 激发是光-羰基加成的原因,而
乙酰乙酸酯烯醇形式的 n-π* 和 π-π* 吸收在同一区域,因此在照射
乙酰乙酸酯烯醇形式时无法获得有效的 n-π* 激发。