The chemical equivalence of the hydroxy groups in the 5,7-dihydroxycoumarin core has challenged synthetic chemists to develop short and efficient strategies for the selective modification of one of the hydroxy groups leaving the second intact. Over the past 100 years, chemists have proposed various approaches to distinguishing between these two groups according to their reactivity. While the early syntheses included simple nonselective reactions of both hydroxy groups and the subsequent separation of mixtures of the 5-O- and 7-O-isomers formed, recent sophisticated approaches often include the introduction of protective groups for selective directing reactions or the completely controlled construction of the 5,7-dihydroxycoumarin framework by Horner–Wadsworth–Emmons reaction. This review discusses in detail approaches towards unsymmetrically substituted 5,7-dihydroxycoumarins as well as factors influencing 5-O vs. 7-O regioselectivity of reactions of 5,7-dihydroxycoumarins. This review covers all the literature since 1921 with an emphasis on recent works. This critical review may facilitate the synthesis of new drug candidates as well as the total synthesis of natural products.

中文翻译：

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不对称取代的5,7-二羟基香豆素的合成方法

5,7-二羟基香豆素核心中羟基的化学等效性已对合成化学家提出了挑战，要求他们开发出短而有效的策略来选择性修饰其中一个羟基，而使第二个完整。在过去的100年中，化学家们提出了各种根据反应性来区分这两组的方法。早期的合成包括两个羟基的简单非选择性反应以及随后的5- O-和7- O混合物的分离-异构体的形成，最近的复杂方法通常包括引入用于选择性引导反应的保护基，或通过霍纳-沃兹沃思-埃蒙斯反应完全控制5,7-二羟基香豆素骨架的构建。这篇综述详细讨论了非对称取代的5,7-二羟基香豆素的制备方法，以及影响5,7-二羟基香豆素反应的5- O和7- O区域选择性的因素。这篇综述涵盖了自1921年以来的所有文献，重点是近期著作。严格的审查可能会促进新药候选物的合成以及天然产物的总合成。