Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), CSIC-Universidad de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain.
Supramolecular Organic and Organometallic Chemistry Centre (SOOMCC), Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, 400028 Cluj-Napoca, Romania.
Int J Mol Sci. 2023 Apr 20;24(8):7583. doi: 10.3390/ijms24087583.
The irradiation of 2-aryl-4-(-3'-aryl-allylidene)-5(4)-oxazolones with blue light (456 nm) in the presence of Ru(bpy) (bpy = 2,2'-bipyridine, 5% mol) gives the unstable cyclobutane-bis(oxazolones) by [2+2]-photocycloaddition of two oxazolones . Each oxazolone contributes to the formation of with a different C=C bond, one of them reacting through the exocyclic C=C bond, while the other does so through the styryl group. Treatment of unstable cyclobutanes with NaOMe/MeOH produces the oxazolone ring opening reaction, affording stable styryl-cyclobutane bis(amino acids) . The reaction starts with formation of the T excited state of the photosensitizer [Ru*(bpy)], which reacts with S of oxazolones through energy transfer to give the oxazolone T state (oxa*)-, which is the reactive species and was characterized by transient absorption spectroscopy. Measurement of the half-life of (oxa*)- for , and shows large values for and (10-12 μs), while that of is shorter (726 ns). Density functional theory (DFT) modeling displays strong structural differences in the T states of the three oxazolones. Moreover, study of the spin density of T state (oxa*)- provides clues to understanding the different reactivity of 4-allylidene-oxazolones described here with respect to the previously reported 4-arylidene-oxazolones.
2-芳基-4-(-3'-芳基-烯丙基)-5(4)-恶唑酮在Ru(bpy)（bpy=2,2'-联吡啶，5%mol）存在下用蓝光（456nm）照射，通过两个恶唑酮的[2+2]-光环加成反应生成不稳定的环丁烷-双（恶唑酮）。每个恶唑酮以不同的 C=C 键参与的形成，其中一个通过环外 C=C 键反应，而另一个则通过苯乙烯基基团反应。不稳定的环丁烷与 NaOMe/MeOH 处理会产生恶唑酮开环反应，生成稳定的苯乙烯-环丁烷双（氨基酸）。反应从光敏剂[Ru*(bpy)]的 T 激发态开始，它通过能量转移与恶唑酮的 S 反应，生成恶唑酮的 T 态（oxa*）-，这是反应性物质，并通过瞬态吸收光谱进行了表征。测量（oxa*）-对于 、和的半衰期表明和具有较大的值（10-12μs），而的半衰期较短（726ns）。密度泛函理论（DFT）建模显示了三种恶唑酮 T 态的结构差异很大。此外，T 态（oxa*）-的自旋密度研究为理解此处描述的 4-烯丙基恶唑酮与先前报道的 4-芳基恶唑酮的不同反应性提供了线索。
