Abstract

The imidazo[1,2-a]pyridine moiety is present in drugs with several biological activities. The most direct way of obtaining this nucleus is the Groebke–Blackburn–Bienaymé three-component reaction (GBB-3CR) between aminopyridines, aldehydes, and isocyanides under both Lewis and Brønsted acid catalysis. However, several catalysts for this reaction have major drawbacks such as being expensive, extremely dangerous, strong oxidizing, and even explosive. In this scenario, heteropolyacids emerge as greener and safer alternatives due to their very strong Brønsted acidity. In particular, phosphotungstic acid (HPW) is an economical and green attractive catalyst for being cheap, non-toxic, and is known for its chemical and thermal stability. Herein, we report a straightforward approach to the GBB-3CR using HPW as catalyst in ethanol under microwave (μw) heating. This convenient environmentally benign methodology is broad in scope, provides the heterobicyclic products in high yields (up to 99%), with a low catalyst loading (2 mol %) in only 30 minutes, and allows the successful use of aliphatic aldehydes, substrates not so frequently explored with most usual catalysts for this reaction. Furthermore, the aforementioned advantages make this methodology very attractive and superior to the existing ones.

Beilstein J. Org. Chem. 2024, 20, 628–637. doi:10.3762/bjoc.20.55

摘要

咪唑并[1,2- a ]吡啶部分存在于具有多种生物活性的药物中。获得该核的最直接方法是在路易斯酸和布朗斯台德酸催化下，氨基吡啶、醛和异氰化物之间发生 Groebke-Blackburn-Bienaymé 三组分反应 (GBB-3CR)。然而，用于该反应的几种催化剂都存在重大缺点，例如昂贵、极其危险、强氧化性甚至爆炸。在这种情况下，杂多酸因其非常强的布朗斯台德酸性而成为更环保、更安全的替代品。特别是，磷钨酸（HPW）是一种经济且具有绿色吸引力的催化剂，其廉价、无毒，并以其化学和热稳定性而闻名。在此，我们报告了一种在微波 (μw) 加热下使用 HPW 作为乙醇中的催化剂来制备 GBB-3CR 的简单方法。这种方便的环境友好方法适用范围广泛，可在 30 分钟内以高收率（高达 99%）提供杂双环产物，催化剂负载量低（2 mol%），并且可以成功使用脂肪醛，而不是底物。经常用最常见的催化剂来探索该反应。此外，上述优点使该方法非常有吸引力并且优于现有方法。

贝尔斯坦 J. 组织。化学。 2024, 20, 628–637。doi:10.3762/bjoc.20.55