Regioselective Substitution of Heteroaromatic Compounds by Homogeneous Catalysis

已知多种杂环化合物的衍生物具有药理活性。芳基取代杂芳烃不仅是重要的医药试剂，也是π偶联的功能材料，如荧光染料和有机半导体。因此，开发新的、有效的方法将芳基取代基引入杂芳烃是一个重要的课题。本项目的目标是开发更通用和更有效的钯催化杂芳烃直接芳基化反应的新方案。研究发现，大体积的叔膦化合物可以有效地促进2-位和5-位的噻吩类和噻唑类化合物的反应。在某些情况下，铜(I)物种起到了有效的助催化剂作用。观察到3位含吸电子基团的噻吩类化合物不仅在2位和5位发生芳基化反应，而且还在4位发生芳基化反应，得到三芳基的噻吩衍生物。此外，还发现2-噻吩甲酰胺发生三芳化反应并伴随脱氨基化反应生成2，3，5-三芳基硫代苯类化合物。后一种反应也可应用于相应的噻唑、呋喃和恶唑羧胺。并对上述产物的光学性质进行了测试。值得注意的是，一种在分子中具有相当大扭转量的二硫吩衍生物显示出超过40%的荧光量子产率。在进行这项工作的过程中，还开发了其他一些独特的芳基化反应。它们的应用还有待进一步研究。

Various derivatives of heteroaromatic compounds are known to exhibit pharmacological activities. Aryl-substituted heteroaromatics are of importance not only as medicinal agents, but also π-conjugated functional materials such as fluorescent dyes and organic semiconductors. Thus, the development of new, efficient methods for introducing aryl-substituent to heteroaromatics is an important subject. The objective of this project is to develop new protocols that are more general and efficient for the direct arylation of heteroaromatics by means of palladium-catalysis.It was found that bulky tert-phosphines can effectively promote the reaction of thiophenes and thiazoles at the 2-and 5-positions. In some cases, copper(I) species acted as effective cocatalysts. Thiophenes having an electron-withdrawing group at the 3-position was observed to undergo arylation not only at 2-and 5 positions, but also at 4-position to give the triarylthiophene derivatives. Furthermore, it was discovered that 2-thiophenecarboxamides undergo triarylation accompanied by decarbamoylation to produce 2,3,5-triarylthhiophenes. This latter reaction could also be applied to the corresponding carboxamides of thiazole, furan, and oxazole. The optical properties of the above products were also measured. It was of significant interest that a bithiophene derivative having a considerable torsion in the molecule shows a fluorescent quantum yield more than 40%. During the performance this work, some other unique arylation reactions were also developed. The application of them will be investigated further.