Isoxazolone derivatives show significant biological and medicinal properties. They constitute excellent intermediates for the synthesis of numerous heterocycles and undergo several chemical transformations. A literature review shows that the best method for the synthesis of these molecules is a three-component reaction among aromatic aldehydes, ethyl acetoacetate and hydroxylamine hydrochloride under different catalysts and conditions. In continuing our research on new simple and environmentally friendly procedures for the preparation of heterocycles by multi-component reactions, we now report the synthesis of 4-arylmethylideneisoxazol-5(4H)-ones by the reaction among aromatic aldehydes, ethyl acetoacetate and hydroxylamine hydrochloride catalyzed by K2CO3. This commonly available base is very inexpensive, well-tolerated in organic agriculture, and safe; it has found wide use in numerous chemical transformations. Scheme 1 below shows the approach taken. We chose as our model system an equimolar mixture of 4-hydroxybenzaldehyde, ethyl acetoacetate and hydroxylamine chloride in a reaction catalyzed by different amounts of K2CO3. The selected model was subjected to different solvent and temperature conditions, as shown in Table 1. The best result was observed in Entry 8, with 5mol% catalyst in water at reflux for an hour (see Experimental Section). The optimum reaction conditions were applied to a number of aromatic and heteroaromatic aldehydes bearing different substituents. The results are summarized in Table 2. Reaction times were determined by thin layer chromatography in each case. Whatever the position of the substituent, yields were generally good to very good (between 64% and 85% and an average of 69%). Compounds 4k-4m are novel and reported here for the first time.

中文翻译：

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4-Arylmethylideneisoxazol-5(4H)-ones 的简便合成和抗氧化评价

异恶唑酮衍生物显示出显着的生物学和药用特性。它们构成了合成众多杂环的极好中间体，并进行了多次化学转化。文献综述表明，合成这些分子的最佳方法是芳醛、乙酰乙酸乙酯和盐酸羟胺在不同催化剂和条件下的三组分反应。在继续研究通过多组分反应制备杂环的简单且环保的新方法时，我们现在报告了通过芳香醛、乙酰乙酸乙酯和盐酸羟胺反应合成 4-芳基亚甲基异恶唑-5(4H)-酮由 K2CO3 催化。这种常用的碱非常便宜，在有机农业中耐受性良好，并且安全；它已广泛用于许多化学转化。下面的方案 1 显示了所采用的方法。我们选择了 4-羟基苯甲醛、乙酰乙酸乙酯和羟胺氯化物的等摩尔混合物作为我们的模型系统，该反应由不同量的 K2CO3 催化。所选模型经受不同的溶剂和温度条件，如表 1 所示。在 Entry 8 中观察到最好的结果，5mol% 催化剂在水中回流 1 小时（参见实验部分）。将最佳反应条件应用于许多带有不同取代基的芳族和杂芳族醛。结果总结在表2中。在每种情况下通过薄层色谱法确定反应时间。无论取代基的位置如何，产量通常从好到非常好（在 64% 到 85% 之间，平均为 69%）。化合物 4k-4m 是新的，这里是第一次报道。