An intermolecular cross-cyclization between salicylaldehydes and indoles for the preparation of chromeno[2,3-b]indole derivatives was successfully developed by using elemental sulfur as the promoter and oxidant. Various chromeno[2,3-b]indoles can be prepared using indoles and salicylaldehydes bearing different functional groups. The preliminary mechanistic investigations demonstrated that elemental sulfur not only acted as an additional oxidant but also facilitated the reactivity of the 3-position of indole.

中文翻译：

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元素硫促进了吲哚3-位在铬诺[2,3- b ]吲哚结构上的反应性†

以元素硫为促进剂和氧化剂，成功开发了水杨醛与吲哚之间的分子间交叉环化反应，用于制备铬诺[2,3- b ]吲哚衍生物。可以使用带有不同官能团的吲哚和水杨醛制备各种chromeno [2,3- b ]吲哚。初步的机械研究表明，元素硫不仅充当了额外的氧化剂，而且还促进了吲哚3位的反应性。