Mechanistic insights into boron-catalysed direct amidation reactions.
Mechanistic insights into boron-catalysed direct amidation reactions.
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DOI：
10.1039/c7sc03595k
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发表时间：
2018-01-28
期刊：
影响因子：
8.4
通讯作者：
Whiting A
中科院分区：
文献类型：
--
作者：
Arkhipenko S;Sabatini MT;Batsanov AS;Karaluka V;Sheppard TD;Rzepa HS;Whiting A
在这项研究中，普遍接受的硼催化直接酰胺化的单酰氧基硼机制的问题，并提出了新的替代方案。在这项研究中，普遍接受的硼催化直接酰胺化的单酰氧基硼机制的问题，并提出了新的替代方案。我们已经进行了详细的调查硼催化的酰胺化反应，通过胺/羧酸和硼酸，硼酸和硼酸之间的相互作用的研究，并已分离和表征的NMR/X-射线晶体学的许多可能的中间体存在于催化酰胺化反应。在所有情况下，观察到胺和硼化合物之间的快速反应，并提出这种硼-氮相互作用是非常可能发生在催化酰胺化反应。这些研究还清楚地表明，硼酸不是酰胺化的合适催化剂，因为它们要么形成不反应的氨基羧酸盐络合物，要么经历脱硼反应得到硼酸。因此，似乎硼原子上的至少三个自由配位位点对于酰胺化催化的发生是必需的。然而，这些观察结果是不一致的硼介导的酰胺化反应，涉及亲核攻击的胺到单体酰氧基硼中间体，目前公认的“机制”，作为我们的观察和理论建模的结果，替代提出的机制硼介导的酰胺化反应。这些可能通过形成二聚体B-X-B基序（X = O，NR）来进行，其独特地能够提供羧酸的活化，同时协调胺亲核试剂向羰基的递送。在B3 LYP +D3/Def 2-TZVPP水平（溶剂= CH 2Cl 2）的催化循环的量子力学计算支持几个密切相关的潜在途径的酰胺化的建议，所有这些都可能是低于目前公认的机制的能量。
The generally accepted monoacyloxyboron mechanism of boron-catalysed direct amidation is brought into question in this study, and new alternatives are proposed. The generally accepted monoacyloxyboron mechanism of boron-catalysed direct amidation is brought into question in this study, and new alternatives are proposed. We have carried out a detailed investigation of boron-catalysed amidation reactions, through study of the interaction between amines/carboxylic acids and borinic acids, boronic acids and boric acid, and have isolated and characterised by NMR/X-ray crystallography many of the likely intermediates present in catalytic amidation reactions. Rapid reaction between amines and boron compounds was observed in all cases, and it is proposed that such boron–nitrogen interactions are highly likely to take place in catalytic amidation reactions. These studies also clearly show that borinic acids are not competent catalysts for amidation, as they either form unreactive amino-carboxylate complexes, or undergo protodeboronation to give boronic acids. It therefore seems that at least three free coordination sites on the boron atom are necessary for amidation catalysis to occur. However, these observations are not consistent with the currently accepted ‘mechanism’ for boron-mediated amidation reactions involving nucleophilic attack of an amine onto a monomeric acyloxyboron intermediate, and as a result of our observations and theoretical modelling, alternative proposed mechanisms are presented for boron-mediated amidation reactions. These are likely to proceed via the formation of a dimeric B–X–B motif (X = O, NR), which is uniquely able to provide activation of the carboxylic acid, whilst orchestrating the delivery of the amine nucleophile to the carbonyl group. Quantum mechanical calculations of catalytic cycles at the B3LYP+D3/Def2-TZVPP level (solvent = CH2Cl2) support the proposal of several closely related potential pathways for amidation, all of which are likely to be lower in energy than the currently accepted mechanism.
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DOI：
10.1002/anie.201508983
发表时间：
2016-02-05
期刊：
Angewandte Chemie (International ed. in English)
影响因子：
--
作者：
Burés J
通讯作者：
Burés J
影响因子：
8.4
作者：
Ishihara K;Lu Y
通讯作者：
Lu Y
影响因子：
16.6
作者：
Bures, Jordi
通讯作者：
Bures, Jordi
影响因子：
5.4
作者：
Arnold, Kenny;Davies, Bryan;Whiting, Andrew
通讯作者：
Whiting, Andrew
影响因子：
16.6
作者：
Arnold, Kenny;Davies, Bryan;Whiting, Andrew
通讯作者：
Whiting, Andrew