Herein we report a facile synthesis of tetracyclic fluorenopyrans from simple acyclic reactants, propargyl alcohols and 3‐methylpentane‐2,4‐dione under calcium catalysis. This one‐pot, 3‐component reaction proceeds through a sequential allene formation, Friedel‐Crafts cyclization/cycloisomerization, intramolecular aldol reaction, Claisen rearrangement, and 6‐endo dig cyclization to result in the formation of fluorenopyrans (indeno[2,1‐g]chromenes). This strategy was further used in the synthesis of 3‐iodo‐fluorenopyrans, by adding iodocyclization to the above sequence of reactions (4‐CR). Noticeably, this highly practical, atom and the step‐economic procedure is catalyzed by a sustainable (alkaline earth) metal salt and tolerates the broad substrate scope, allowing the further transformations and synthetic utilities of these complex polycyclic moieties.

中文翻译：

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Ca（II）介导的无环化合物向多环氟吡喃的区域选择性单锅顺序环化

本文报道了钙催化下由简单的无环反应物，炔丙醇和3-甲基戊烷-2,4-二酮轻松合成四环氟吡喃的方法。这一单锅，三组分反应通过依次进行的烯丙基形成，Friedel-Crafts环化/环异构化，分子内羟醛反应，Claisen重排和6-内挖来进行环化导致形成氟吡喃（茚并[2,1–g]色烯）。通过将碘环化作用添加到上述反应序列中（4-CR），该策略被进一步用于3-碘-芴吡喃的合成。值得注意的是，这种高度实用的原子和分步经济程序受到可持续的（碱土金属）金属盐的催化，并能承受广泛的底物范围，从而允许这些复杂的多环部分的进一步转化和合成应用。