A base-mediated, three-component synthesis of symmetric and unsymmetric pyran-fused biscoumarins via the coupling of 4-hydroxycoumarin with 4-chloro-3-formylcoumarin in ethanol is reported. This methodology is further extended to the construction of various indole/coumarin-substituted symmetric pyran-fused biscoumarins. The unsymmetric pyran-fused biscoumarin can react with amines and 4-hydroxycoumarins under basic and acidic conditions to afford pyridinone-fused coumarins and pyranone-fused coumarins, respectively. The mechanisms of their formation are proposed.

中文翻译：

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吡喃稠合双香豆素的三组分合成：吡啶酮和吡喃酮稠合香豆素入门

报道了通过4-羟基香豆素与 4-氯-3-甲酰基香豆素在乙醇中偶联，碱介导的三组分合成对称和不对称吡喃稠合双香豆素。该方法进一步扩展到各种吲哚/香豆素取代的对称吡喃稠合双香豆素的构建。不对称吡喃稠合双香豆素可以在碱性和酸性条件下与胺和4-羟基香豆素反应，分别得到吡啶酮稠合香豆素和吡喃酮稠合香豆素。提出了它们的形成机制。