In recent years, green chemistry techniques have attracted considerable attention in the chemical industry and academic research laboratories due to environmental, health, and economic benefits. In this context, multi-component domino reactions (MDRs) have considerable ecological interest. They represent a very influential and efficient bondforming strategy for medicinal, organic, and combinatorial chemistry. In this regard, microwave-assisted organic synthesis (MAOS) has developed into a highly-valued field for the preparation of complex heterocyclic molecules. MAOS permits enhanced reaction rates, formation of purer products in higher yields and easier manipulation. Consequently, the design of novel MDRs using microwave irradiation for the synthesis of simple and complex bioactive heterocycles has become a notable topic in the drug discovery process and for the analysis of drugs. Among these drugs, we may note the importance of the pyran and phenazine moieties, particularly where these units may be clubbed together. Some important pharmaceutically active pyrano-fused benzophenazine derivatives are shown in Figure 1. In continuation of our research in the synthesis of complex organic compounds utilizing green chemistry tools, we report here our results on the efficient domino synthesis of novel benzo[a]pyrano[3',4':5,6]pyrano[2,3-c]phenazines 6a-j in a one-pot, four-component condensation reaction between 2-hydroxy-1,4-naphthoquinone 1, o-phenylenediamine 2, benzaldehydes 4 and 4-hydroxy-6-methyl-2H-pyran-2-one 5. The reaction is catalyzed by phosphotungstic acid (H3PW12O40). We have found the latter to be a highly efficient, eco-friendly and recyclable solid heteropolyacid catalyst when used under microwave irradiation (180 W, max. 70 C) in EtOH/H2O (1:1) (Scheme 1).

中文翻译：

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使用 H3PW12O40 作为高效、经济且可回收的催化剂绿色合成新型苯并[a]吡喃并[3',4':5,6]吡喃并[2,3-c]吩嗪的微波辅助多组分多米诺反应

近年来，绿色化学技术由于环境、健康和经济效益等方面的优势，在化工行业和学术研究实验室引起了广泛关注。在这种情况下，多组分多米诺骨牌反应 (MDR) 具有相当大的生态兴趣。它们代表了一种非常有影响力和有效的药物、有机和组合化学成键策略。在这方面，微波辅助有机合成（MAOS）已发展成为制备复杂杂环分子的高价值领域。MAOS 允许提高反应速率，以更高的产率和更容易的操作形成更纯的产品。最后，使用微波辐射设计新型 MDR 以合成简单和复杂的生物活性杂环已成为药物发现过程和药物分析中的一个显着主题。在这些药物中，我们可能会注意到吡喃和吩嗪部分的重要性，特别是在这些单元可能被连接在一起的地方。一些重要的药学活性吡喃稠合苯吩嗪衍生物如图 1 所示。 为了继续我们利用绿色化学工具合成复杂有机化合物的研究，我们在此报告了我们关于高效多米诺合成新型苯并 [a] 吡喃的结果。 3',4':5,6]吡喃并[2,3-c]吩嗪6a-j在2-羟基-1,4-萘醌1、邻苯二胺2、苯甲醛 4 和 4-hydroxy-6-methyl-2H-pyran-2-one 5. 该反应由磷钨酸 (H3PW12O40) 催化。我们发现后者是一种高效、环保且可回收的固体杂多酸催化剂，当在 EtOH/H2O (1:1) 中的微波辐射（180 W，最高 70 C）下使用时（方案 1）。