Institute of Organic Chemistry University of Regensburg Universitätstr. 31 Regensburg 93053 Germany.
Departamento de Química Orgánica Universidad de La Laguna Avda. Astrofísico Francisco Sánchez 3 38206 La Laguna Tenerife Spain.
ChemistryOpen. 2020 May 5;9(6):649-656. doi: 10.1002/open.202000092. eCollection 2020 Jun.
The outcome of photosensitized [2+2]-cycloaddition reactions of various cinnamates has been compared in different reaction media, including homogeneous organic solutions under inert conditions, degassed water, and aerated physical gels. The reactions were performed under LED blue light (λ=455 nm) irradiation and [Ir{dF(CF)ppy}(dtb-bpy)]PF (1.0 mol%) as photocatalyst. The processes were optimized taking into consideration solvent, gelator, and substrate. Comparative kinetics analyses, as well as the effect of the reaction media on the diastereoselectivity of the process, were evaluated during this investigation. In a number of cases, carrying out the reaction in a less polar solvent, like toluene or highly polar solvent, like water had a tremendous impact on the diastereoselectivity of the process, pointing towards an effect on the stabilization of the putative diradical intermediate in this medium. Moreover, while for reactions run in homogeneous solution oxygen needs to be excluded, no erosion in yield is observed when the photoadditions were run in aerated gel media.
各种肉桂酸的光致敏[2+2]-环加成反应的结果已在不同的反应介质中进行了比较，包括惰性条件下的均相有机溶液、除气水和充气物理凝胶。反应在 LED 蓝光（λ=455nm）照射下进行，并使用[Ir{dF（CF）ppy}（dtb-bpy）]PF（1.0mol%）作为光催化剂。在考虑溶剂、凝胶剂和底物的情况下对这些过程进行了优化。在研究过程中，对比较动力学分析以及反应介质对该过程非对映选择性的影响进行了评估。在许多情况下，在非极性溶剂（如甲苯）或极性更强的溶剂（如水）中进行反应对该过程的非对映选择性有巨大影响，这表明该介质可能对假定的自由基中间体的稳定性有影响。此外，虽然对于在均相溶液中进行的反应需要排除氧气，但当在充气凝胶介质中进行光加成反应时，产率没有下降。
