Synthesis of Diversely Functionalized 2H‑Chromenes through Pd-Catalyzed Cascade Reactions of 1,1-Dibromoolefin Derivatives with Arylboronic Acids

In this work, an unprecedented synthesis of (2H-chromen-2-ylidene)­acetates and (2H-chromen-2-ylidene)­ethanones with controlled stereoselectivity via Pd-catalyzed cascade reactions of 3-(2-(2,2-dibromovinyl)­phenoxy)­acrylates or 3-(2-(2,2-dibromovinyl)­phenoxy)­enones with aryl boronic acids has been established. This protocol combines two C–C bond forming reactions (an intermolecular Suzuki coupling followed by an intramolecular Heck coupling) in one pot under the catalysis of the same catalyst. Compared with literature methods for the preparation of 2H-chromene derivatives, it has advantages such as easily obtainable or commercially available substrates, diverse substitution pattern of products, simple procedure, and excellent stereoselectivity. Interestingly, this cascade reaction could distinguish the subtle difference of the electron-withdrawing capacity and the size of various functional groups and thus resulted in a different chemoselectivity. In addition, the utility of the (2H-chromen-2-ylidene)­acetate thus obtained was showcased by its facile transformation into the synthetically and photophysically significant 3H-xanthen-3-one derivative.

本研究建立了一种前所未有的合成方法，通过钯（Pd）催化的级联反应，以3-(2-(2,2-二溴乙烯基)苯氧基)丙烯酸酯或3-(2-(2,2-二溴乙烯基)苯氧基)烯酮与芳基硼酸(aryl boronic acids)为底物，实现了具有可控立体选择性的(2H-色烯-2-亚基)乙酸酯((2H-chromen-2-ylidene)acetates)与(2H-色烯-2-亚基)乙酮((2H-chromen-2-ylidene)ethanones)类化合物的合成。该策略在单一催化剂催化的一锅反应中，整合了两步C-C键构建过程——依次为分子间Suzuki偶联（Suzuki coupling）与分子内Heck偶联（Heck coupling）。相较于现有文献中制备2H-色烯(2H-chromene)衍生物的方法，本方法具有底物易于获取或商业可得、产物取代模式多样、操作简便以及立体选择性优异等优势。值得注意的是，该级联反应可区分不同官能团吸电子能力与空间尺寸的细微差异，从而展现出差异化的化学选择性(chemoselectivity)。此外，通过将所得的(2H-色烯-2-亚基)乙酸酯便捷转化为在合成与光物理领域均具有重要价值的3H-氧杂蒽-3-酮(3H-xanthen-3-one)衍生物，验证了该类产物的应用价值。