Tetrahydrobenzo[b]pyrans are fused oxygen-containing heterocycles that are found in many biologically active compounds. Therefore, researchers in organic synthesis are searching for suitable, efficient, and useful methods for their synthesis. In this contribution, a series of tetrahydrobenzo[b]pyran derivatives was synthesized using aryl aldehydes, malononitrile, and cyclohexane-1,3-dione or dimedone as the available starting materials. The three-component reactions were catalyzed by 1,3-dibenzyl-1H-benzo[d]imidazol-3-ium chloride as the N-heterocyclic carbene precursor. The heterocyclic oxygen-containing products were obtained in good to excellent isolated yields within relatively shorter reaction times. Optimizing the reaction conditions was performed from the point of view of various parameters of the reaction. The results of these experiments showed that the best solvent system includes water-ethanol, the most suitable reaction temperature is 60ºC, and the optimal amount of the imidazolium catalyst loading is 5 mol%. Operational simplicity, no need for chromatographic methods for purification, simple work-up for pure products, and avoiding hazardous solvents are remarkable features of this three-component reaction. Moreover, in these multicomponent cyclo-condensations, no by-products were observed.

中文翻译：

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1,3-二苄基-1H-苯并[d]咪唑-3-氯化鎓催化合成四氢苯并[b]吡喃

四氢苯并[b]吡喃是稠合的含氧杂环，存在于许多生物活性化合物中。因此，有机合成领域的研究人员正在寻找合适、有效、有用的合成方法。在这项贡献中，使用芳基醛、丙二腈和环己烷-1,3-二酮或双甲酮作为可用起始材料合成了一系列四氢苯并[b]吡喃衍生物。三组分反应由 1,3-二苄基-1H-苯并[d]咪唑-3-氯化鎓作为 N-杂环卡宾前体催化。在相对较短的反应时间内以良好至优异的分离产率获得杂环含氧产物。从反应的各个参数的角度进行反​​应条件的优化。实验结果表明，最佳溶剂体系为水-乙醇，最合适的反应温度为60℃，最佳咪唑鎓催化剂负载量为5 mol%。操作简单、无需色谱法纯化、纯产物处理简单以及避免使用有害溶剂是这种三组分反应的显着特点。此外，在这些多组分环缩合中，没有观察到副产物。