Natural dolomitic limestone (NDL) is employed as a heterogeneous green catalyst for the synthesis of medicinally valuable benzimidazoles, dihydropyrimidinones, and highly functionalized pyridines via C–N, C–C, and C–S bond formations in a mixture of ethanol and H₂O under ultrasound irradiation. The catalyst is characterized by XRD, FTIR, Raman spectroscopy, SEM, and EDAX analysis. The main advantages of this methodology include the wide substrate scope, cleaner reaction profile, short reaction times, and excellent isolated yields. The products do not require chromatographic purification, and the catalyst can be reused seven times. Therefore, the catalyst is a greener alternative for the synthesis of the above N-heterocycles compared to the existing reported catalysts.

中文翻译：

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在超声辐射下，天然白云石石灰石催化合成苯并咪唑，二氢嘧啶酮和高度取代的吡啶。

天然白云质石灰石（NDL）被用作异质绿色催化剂，用于通过乙醇和H ₂的混合物中C–N，C–C和C–S键的形成来合成具有药用价值的苯并咪唑，二氢嘧啶酮和高度官能化的吡啶O在超声波照射下。该催化剂通过XRD，FTIR，拉曼光谱，SEM和EDAX分析来表征。这种方法的主要优点包括广泛的底物范围，更清洁的反应曲线，较短的反应时间和优异的分离产率。该产品不需要色谱纯化，该催化剂可以重复使用七次。因此，与现有报道的催化剂相比，该催化剂是用于合成上述N-杂环的更绿色的替代物。