Institute of Chemistry, University of Silesia in Katowice, ul. Szkolna 9, PL-40007 Katowice, Poland.
Institute of Polymer and Dye Technology, Lodz University of Technology, Stefanowskiego 12/16, 90-924 Lodz, Poland.
Molecules. 2020 Apr 28;25(9):2053. doi: 10.3390/molecules25092053.
A new approach to the synthesis of selected quinolinecarbaldehydes with carbonyl groups located at C5 and/or in C7 positions is presented in this paper in conjunction with spectroscopic characterization of the products. The classical Reimer-Tiemann, Vilsmeier-Haack and Duff aldehyde synthesis methods were compared due to their importance. Computational studies were carried out to explain the preferred selectivity of the presented formylation transformations. A carbene insertion reaction based on Reimer-Tiemann methodology is presented for making 7-bromo-8-hydroxyquinoline-5-carbaldehyde. Additionally, Duff and Vilsmeier-Haack reactions were used in the double formylation of quinoline derivatives and their analogues benzo[]quinolin-10-ol, 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde, 8-(dimethylamino) quinoline-5,7-dicarbaldehyde and 10-hydroxybenzo[h]quinoline-7,9-dicarbaldehyde. Four Schiff base derivatives of 2,6-diisopropylbenzenamine were prepared from selected quinoline-5-carbaldehydes and quinoline-7-carbaldehyde by an efficient synthesis protocol. Their properties have been characterized by a combination of several techniques: MS, HRMS, GC-MS, FTIR, electronic absorption spectroscopy and multinuclear NMR. The electrochemical properties of 8-hydroxy-quinoline-5-carbaldehyde, 6-(dimethylamino)quinoline-5-carbaldehyde and its methylated derivative were investigated, and a strong correlation between the chemical structure and obtained reduction and oxidation potentials was found. The presence of a methyl group facilitates oxidation. In contrast, the reduction potential of methylated compounds was more negative comparing to non-methylated structure. Calculations of frontier molecular orbitals supported the finding. The structures of 8-hydroxy-2-methylquinoline-5,7-dicarbaldehyde and four Schiff bases were determined by single-crystal X-ray diffraction measurements.
本文提出了一种新的方法，用于合成具有羰基位于 C5 和/或 C7 位置的选定喹啉醛，同时对产物进行了光谱特征描述。由于其重要性，对经典的 Reimer-Tiemann、Vilsmeier-Haack 和 Duff 醛合成方法进行了比较。进行了计算研究以解释所提出的甲酰化转化的优先选择性。基于 Reimer-Tiemann 方法提出了用于合成 7-溴-8-羟基喹啉-5-甲醛的卡宾插入反应。此外，Duff 和 Vilsmeier-Haack 反应用于喹啉衍生物及其类似物苯并[]喹啉-10-醇、8-羟基-2-甲基喹啉-5,7-二甲醛、8-(二甲基氨基)喹啉-5,7-二甲醛和 10-羟基苯并[h]喹啉-7,9-二甲醛的双甲酰化。从选定的喹啉-5-醛和喹啉-7-醛通过有效的合成方案制备了四种 2,6-二异丙基苯甲胺的席夫碱衍生物。通过几种技术的组合对它们的性质进行了表征：MS、HRMS、GC-MS、FTIR、电子吸收光谱和多核 NMR。研究了 8-羟基喹啉-5-甲醛、6-(二甲基氨基)喹啉-5-甲醛及其甲基化衍生物的电化学性质，发现化学结构与获得的还原和氧化电位之间存在很强的相关性。甲基的存在有利于氧化。相比之下，与非甲基化结构相比，甲基化化合物的还原电位更负。前沿分子轨道的计算支持了这一发现。通过单晶 X 射线衍射测量确定了 8-羟基-2-甲基喹啉-5,7-二甲醛和四个席夫碱的结构。
