Mediation of conformationally controlled photodecarboxylations of chiral and cyclic aryl esters by substrate structure, temperature, pressure, and medium constraints.
Mediation of conformationally controlled photodecarboxylations of chiral and cyclic aryl esters by substrate structure, temperature, pressure, and medium constraints.
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DOI：
10.1021/ja049688w
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发表时间：
2004-07
影响因子：
15
通讯作者：
Tadashi Mori;R. Weiss;Y. Inoue
中科院分区：
文献类型：
--
作者：
Tadashi Mori;R. Weiss;Y. Inoue
一种芳基链烷酸酯，2，4，6-三甲基苯基（S）-（+）-2-甲基丁酸酯，其酯基在羰基碳的α位有一个手性中心，其中光-弗里斯重排被甲基取代基阻断，在各种条件下进行容易的光脱羧反应，并完全保留构型。事实上，脱羧过程具有许多表面上[1，3] σ迁移重排的性质。该过程需要协同挤出二氧化碳的螺内酯过渡态，这已被调查使用高层次的DFT和CIS计算：热不太稳定的S-顺式构象在地面和激发单重态发挥重要作用，在确定竞争效率的过程。构象控制也通过底物结构、溶剂相互作用、温度和施加外部压力以及使用约束介质如环糊精和聚乙烯膜来施加。结果与不同温度下的稳态和动态荧光测量相关，以进一步研究基态和激发单重态构象对芳基酯不同光反应性通道的影响程度。
An aryl alkanoate, 2,4,6-trimethylphenyl (S)-(+)-2-methylbutyrate, whose ester group has a chiral center alpha to the carbonyl carbon and in which photo-Fries rearrangements are blocked by methyl substituents, undergoes facile photodecarboxylation under a variety of conditions and with complete retention of configuration. In fact, the decarboxylation process has many of the attributes of a symmetry-allowed suprafacial [1,3]sigmatropic rearrangement. The process requires concerted extrusion of carbon dioxide in a spiro-lactonic transition state, which has been investigated using high level DFT and CIS calculations: thermally less stable s-cis conformers in the ground and excited singlet states play an important role in determining the competitive efficiency of the process. Conformational control has also been imposed by substrate structure, solvent interactions, temperature, and applying external pressure, as well as using constraining media such as cyclodextrins and polyethylene films. The results are correlated with steady-state and dynamic fluorescence measurements at various temperatures in order to investigate further degrees to which ground and excited singlet state conformations affect the different photoreactivity channels available to the aryl esters.