Institute for Organic Chemistry, Westfälische Wilhelms-Universität Münster , Corrensstrasse 40, 48149 Münster, Germany.
J Am Chem Soc. 2015 Sep 9;137(35):11254-7. doi: 10.1021/jacs.5b07136. Epub 2015 Aug 28.
Herein, Nature's flavin-mediated activation of complex (poly)enes has been translated to a small molecule paradigm culminating in a highly (Z)-selective, catalytic isomerization of activated olefins using (-)-riboflavin (up to 99:1 Z/E). In contrast to the prominent Z → E isomerization of the natural system, it was possible to invert the directionality of the isomerization (E → Z) by simultaneously truncating the retinal scaffold, and introducing a third olefin substituent to augment A1,3-strain upon isomerization. Consequently, conjugation is reduced in the product chromophore leading to a substrate/product combination with discrete photophysical signatures. The operationally simple isomerization protocol has been applied to a variety of enone-derived substrates and showcased in the preparation of the medically relevant 4-substituted coumarin scaffold. A correlation of sensitizer triplet energy (ET) and reaction efficiency, together with the study of additive effects and mechanistic probes, is consistent with a triplet energy transfer mechanism.
本文将自然界黄素介导的（多）烯复合物激活转化为小分子范例，最终使用（-）核黄素（高达 99:1 的 Z/E 选择性）实现了活化烯烃的高度（Z）-选择性催化异构化。与天然系统中突出的 Z→E 异构化相反，通过同时截断视黄醛支架，并引入第三个烯烃取代基来增加异构化时的 A1,3-应变，可以反转异构化的方向（E→Z）。因此，产物发色团中的共轭减少，导致具有离散光物理特征的底物/产物组合。这种操作简单的异构化方案已应用于各种烯酮衍生的底物，并在医学相关的 4-取代香豆素支架的制备中得到了展示。敏化剂三重态能量 (ET) 和反应效率的相关性，以及添加剂效应和机理探针的研究，与三重态能量转移机制一致。
