Yamada Shinji, Nojiri Yuka
Department of Chemistry, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan.
Molecules. 2017 Mar 20;22(3):491. doi: 10.3390/molecules22030491.
Irradiation of (E)-4-(2-(2-naphthyl)vinyl)pyridine (1a) and (E)-4-(2-(1-naphthyl)vinyl)pyridine (1b) with a 250 W high-pressure mercury lamp in acidic solution afforded synHT dimers in high stereoselectivities. Similar results were obtained by visible light irradiation. On the other hand, when the reactions were carried out under neutral conditions, the stereoselectivities were very low, and the yields were decreased by visible light irradiation. Comparison of the UV-vis spectra between the acidic and the neutral conditions elucidated that the red shift was observed in acidic solutions. These results show that HCl plays essential roles not only in the preorientation of substrates through cation-π interactions, but also in the changes in the absorption properties of substrates that enable visible light reactions.
在酸性溶液中，用250W高压汞灯照射（E）-4-（2-（2-萘基）乙烯基）吡啶（1a）和（E）-4-（2-（1-萘基）乙烯基）吡啶（1b），可高立体选择性地得到顺式HT二聚体。通过可见光照射也得到了类似的结果。另一方面，当反应在中性条件下进行时，立体选择性非常低，并且可见光照射会降低产率。酸性和中性条件下紫外可见光谱的比较表明，在酸性溶液中观察到了红移。这些结果表明，HCl不仅通过阳离子-π相互作用在底物的预取向中起重要作用，而且在使可见光反应成为可能的底物吸收特性变化中也起重要作用。
