Luo Hao, Liu Fang-Zi, Liu Yan, Chu Zhaoyang, Yan KaKing
School of Physical Science and Technology, ShanghaiTech University, 201210 Shanghai, China.
J Am Chem Soc. 2023 Jul 19;145(28):15118-15127. doi: 10.1021/jacs.3c00614. Epub 2023 Jul 10.
Precise control in reaction selectivity is the goal in modern organic synthesis, and it has been widely studied throughout the synthetic community. In comparison, control of divergent reactivity of a given reagent under different reaction conditions is relatively less explored aspect of chemical selectivity. We herein report an unusual reaction between polycyclic aromatic hydrocarbons and periodic acid HIO (), where the product outcome is dictated by the choice of reaction conditions. That is, reactions under solution-based condition give preferentially C-H iodination products, while reactions under solvent-free mechanochemical condition provide C-H oxidation quinone products. Control experiments further indicated that the iodination product is not a reaction intermediate toward the oxidation product and vice versa. Mechanistic studies unveiled an in situ crystalline-to-crystalline phase change in during ball-milling treatment, where we assigned it as a polymeric hydrogen-bond network of . We believe that this polymeric crystalline phase shields the more embedded electrophilic ═O group of from C-H iodination and bias a divergent C-H oxidation pathway (with I═) in the solid state. Collectively, this work demonstrates that mechanochemistry can be employed to completely switch a reaction pathway and unmask hidden reactivity of chemical reagents.
精确控制反应选择性是现代有机合成的目标，并且在整个合成领域都得到了广泛研究。相比之下，在不同反应条件下控制给定试剂的发散反应性是化学选择性中相对较少被探索的方面。我们在此报告了多环芳烃与高碘酸HIO（）之间的一种不寻常反应，其中产物结果取决于反应条件的选择。也就是说，基于溶液的条件下反应优先得到C-H碘化产物，而无溶剂机械化学条件下的反应则提供C-H氧化醌产物。对照实验进一步表明，碘化产物不是氧化产物的反应中间体，反之亦然。机理研究揭示了球磨处理过程中 原位的晶态到晶态的相变，我们将其归因于 的聚合物氢键网络。我们认为，这种聚合物晶相屏蔽了 中嵌入更深的亲电═O基团，使其不发生C-H碘化反应，并在固态下偏向于发散的C-H氧化途径（生成I═）。总的来说，这项工作表明机械化学可用于完全切换反应途径并揭示化学试剂隐藏的反应性。
