Key Laboratory of Green Chemistry and Technology of Ministry of Education, College of Chemistry, Sichuan University, 29 Wangjiang Road, 610064, Chengdu, PR China.
School of Chemistry and Chemical Engineering, Chongqing University, 400030, Chongqing, PR China.
Nat Commun. 2019 Dec 11;10(1):5664. doi: 10.1038/s41467-019-13611-6.
Transition metal-catalyzed C-H activation and radical reactions are two versatile strategies to construct diverse organic skeletons. Here we show the construction of a class of flavylium fluorophores via the merge of radical chemistry and C-H activation starting from (hetero)aryl ketones and alkynes. This protocol is not only applicable to aryl ketones but also to heteroaryl ketones such as thiophene, benzothiophene and benzofuran, thus leading to structural diversity. Mechanism studies, including control experiments, intermediate separation, radical trapping, EPR and ESI-HRMS experiments, demonstrate that the key step lies in the addition of the acyl radical generated by the copper-catalyzed C-C bond cleavage of aryl ketone to the rhodacycle formed via the C-H activation of aryl ketone. The flavylium fluorophores feature butterfly symmetrical configuration, nearly planar skeleton and delocalized positive charge, and exhibit intriguing photophysical properties, such as tunable absorption and emission wavelengths and high quantum yields.
过渡金属催化的 C-H 活化和自由基反应是构建各种有机骨架的两种通用策略。在这里，我们展示了通过自由基化学和 C-H 活化的结合，从（杂）芳基酮和炔烃出发构建一类 flavylium 荧光团的方法。该方法不仅适用于芳基酮，也适用于噻吩、苯并噻吩和苯并呋喃等杂芳基酮，从而实现了结构的多样性。包括对照实验、中间体分离、自由基捕获、EPR 和 ESI-HRMS 实验在内的机理研究表明，关键步骤在于铜催化的芳基酮 C-C 键断裂生成的酰基自由基与芳基酮 C-H 活化形成的 rhodacycle 的加成。flavylium 荧光团具有蝶形对称结构、近平面骨架和离域正电荷，表现出有趣的光物理性质，如可调的吸收和发射波长以及高量子产率。
