In view of our ongoing interest in nanocatalysis, multicomponent reactions (MCR) and solvent free synthesis, we have developed a new procedure for the preparation of quinolines. The procedure involves substituted aromatic anilines, aldehydes and acetophenone and is catalyzed by CeO2-TiO2 under solvent-free conditions (Scheme 1). We now present a study on the substrate scope and the effect of temperature, solvent, and catalyst concentration for this environmentally friendly protocol. Aniline (1), benzaldehyde (2) and acetophenone (3) were selected as model substrates to optimize the reaction conditions. The reaction was carried out in several solvents including DMF, toluene, ethanol, 1,4-dioxane and solvent free as summarized in Table 1. Reaction in solvents took longer, and gave lower yields, when compared to the solvent-free reaction. We view this as a fortunate combination of efficiency and green characteristics. In order to investigate the effect of temperature on the reaction, the concentration of catalyst was kept constant at 2wt.% and a mixture of the substrates was heated at temperatures ranging from 30–80 C. The reaction was monitored by TLC under solvent free conditions. After stirring for 360min, no reaction occurred at room temperature. Increasing the reaction temperature to 70 C (Table 2, entry 5) resulted in a better yield and shorter reaction time. Further increases in the temperature did not show any material improvement in the yield or reaction time. Therefore, 70 C was chosen as the reaction temperature for all further reactions. We studied the effect of catalyst concentration on the reaction by varying the amounts of catalyst (0.5, 1, 2, and 5wt. %) at 70 C under solvent-free conditions. According to the results presented in Table 3, in the absence of the CeO2-TiO2, the reaction did not produce any products after refluxing for 70 C for 360min (Table 3, entry 1). The best results were obtained using 1wt. % of CeO2-TiO2 (Table 3, entry 3)

中文翻译：

---

一种在无溶剂条件下使用可回收的 CeO2-TiO2 纳米复合催化剂制备喹啉的新型多组分方法

鉴于我们对纳米催化、多组分反应 (MCR) 和无溶剂合成的持续兴趣，我们开发了一种制备喹啉的新方法。该过程涉及取代的芳香苯胺、醛和苯乙酮，并在无溶剂条件下由 CeO2-TiO2 催化（方案 1）。我们现在对这种环保协议的底物范围和温度、溶剂和催化剂浓度的影响进行研究。选择苯胺 (1)、苯甲醛 (2) 和苯乙酮 (3) 作为模型底物以优化反应条件。反应在几种溶剂中进行，包括 DMF、甲苯、乙醇、1,4-二恶烷和无溶剂，如表 1 中总结的。与无溶剂反应相比，在溶剂中的反应时间更长，产率更低。我们认为这是效率和绿色特性的幸运结合。为了研究温度对反应的影响，催化剂的浓度保持恒定在 2wt.%，底物混合物在 30-80°C 的温度范围内加热。在无溶剂条件下通过 TLC 监测反应. 搅拌360min后，室温下无反应发生。将反应温度提高到 70°C（表 2，条目 5）会导致更好的收率和更短的反应时间。温度的进一步升高并未显示产率或反应时间的任何实质性改进。因此，选择 70°C 作为所有进一步反应的反应温度。我们通过改变催化剂的量（0.5、1、2 和 5wt.%）来研究催化剂浓度对反应的影响。%) 在 70°C 下无溶剂条件下。根据表 3 中的结果，在没有 CeO2-TiO2 的情况下，反应在 70°C 回流 360 分钟后没有产生任何产物（表 3，条目 1）。最好的结果是使用 1wt. CeO2-TiO2 的百分比（表 3，条目 3）