The thermal and boron-catalysed direct amide formation reactions: mechanistically understudied yet important processes
The thermal and boron-catalysed direct amide formation reactions: mechanistically understudied yet important processes
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DOI：
10.1039/b923093a
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发表时间：
2010-01-01
影响因子：
4.9
通讯作者：
Whiting, Andrew
中科院分区：
文献类型：
--
作者：
Charville, Hayley;Jackson, David;Whiting, Andrew
尽管酰胺形成反应是有机化学中的关键基石反应之一，但直接酰胺形成反应既很少使用，也很少探索。对反应的可行性和普遍适用性的接受取决于研究人员通过以下方面的发展将其纳入主流的能力：（1）对反应机理的理解;和（2）在广泛的底物和环境条件下促进反应的催化剂的设计。从世纪关于直接酰胺形成的最早报道开始，关于机理研究的报道相对较少，尽管很明显，直接酰胺形成的难易程度与羧酸和胺的pK（a）之间没有简单的关系，或者羧酸铵盐的形成是否重要。因此，直接酰胺形成历来在较高温度条件下进行。然而，最近，已经开发了化学计量的和催化的硼化合物，其显著降低了直接酰胺形成将进行的反应温度。有限的尝试，在机械研究点形成酰氧基硼酸盐或硼酸盐物种基本上作为混合酸酐，虽然这些系统的确切顺序仍然是明确确定的。
Despite the amide formation reaction being one of the key cornerstone reactions in organic chemistry, the direct amide formation is both little used and little explored. Acceptance of the feasibility and general applicability of the reaction depends upon the ability of researchers to bring it into the mainstream by development of: (1) an understanding of the mechanism of the reaction; and (2) the design of catalysts which promote the reaction on a wide range of substrates and under ambient conditions. From the earliest report of the direct amide formation in the 19th century, there have been relatively few reports of mechanistic studies, though it is clear that there is not a simple relationship between ease of direct amide formation and the pK(a) of the carboxylic acid and amine, or whether salt ammonium carboxylate formation is important. Consequently, direct amide formation has historically been run under higher temperature conditions. However, more recently, stoichiometric and catalytic boron compounds have been developed that considerably reduce the reaction temperatures under which direct amide formation will proceed. Limited attempts at mechanistic studies point to the formation of acyloxyborate or boronate species acting essentially as mixed anhydrides, though the exact order of these systems remains to be categorically determined.