State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University , Changchun, Jilin 130012, China.
J Org Chem. 2018 Feb 2;83(3):1377-1386. doi: 10.1021/acs.joc.7b02886. Epub 2018 Jan 16.
Without the addition of any additives and production of any small molecules, C3-borylated indoles and transfer hydrogenated indolines have been simultaneously achieved by a B(CF)-catalyzed disproportionation reaction of a broad range of indoles with catecholborane. This catalyst system exhibits excellent catalytic performance for practical applications, such as easy scale-up under solvent-free conditions and long catalytic lifetime over ten sequential additions of starting materials. A combined mechanistic study, including isolation and characterization of key reaction intermediates, analysis of the disproportionation nature of the reaction, in situ NMR of the reaction, and analysis of detailed experimental data, has led to a possible reaction mechanism which illustrates pathways for the formation of both major products and byproducts. Understanding the reaction mechanism enables us to successfully suppress side reactions by choosing appropriate substrates and adjusting the amount of catecholborane needed. More importantly, with an elevated reaction temperature, we could achieve the convergent disproportionation reaction of indoles, in which indolines were continuously oxidized to indoles for the next disproportionation catalytic cycle. Near quantitative conversions and up to 98% yields of various C3-selective borylated indoles were achieved, without any additives or H acceptors.
在没有添加任何添加剂和产生任何小分子的情况下，通过 B(CF)催化的广泛吲哚与邻苯二硼烷的歧化反应，同时实现了 C3-硼化吲哚和转移氢化吲哚啉的合成。该催化剂体系在实际应用中表现出优异的催化性能，例如在无溶剂条件下易于放大规模，以及在 10 次连续添加起始原料的情况下具有较长的催化寿命。通过包括关键反应中间体的分离和表征、反应歧化性质的分析、反应的原位 NMR 分析以及详细实验数据的分析在内的综合机理研究，提出了一种可能的反应机理，说明了主要产物和副产物形成的途径。了解反应机理使我们能够通过选择合适的底物和调整邻苯二硼烷的用量来成功抑制副反应。更重要的是，通过提高反应温度，我们可以实现吲哚的收敛歧化反应，其中吲哚啉连续氧化为吲哚，用于下一个歧化催化循环。在没有任何添加剂或 H 接受体的情况下，各种 C3 选择性硼化吲哚的转化率接近定量，产率高达 98%。
