Regioselective Substitution of Heteroaromatic Compounds by Homogeneous Catalysis

各种杂芳香族化合物的衍生物已知具有药理活性。芳基取代的杂芳烃不仅是一种重要的药物，而且是一种重要的π共轭功能材料，如荧光染料和有机半导体。因此，开发新的、高效的方法来引入芳基取代基是一个重要的课题。该项目的目的是开发新的方案，更普遍和有效的直接芳基化的杂芳烃钯催化。发现体积较大的叔膦能有效地促进噻吩与2位和5位噻唑的反应。在某些情况下，铜(I)是有效的助催化剂。在3位上有一个吸电子基团的噻吩不仅在2位和5位上发生芳化，而且在4位上也发生芳化，从而得到三芳基噻吩衍生物。此外，还发现2-噻吩羧基酰胺经过三芳基化和脱氨基化反应生成2,3,5-三芳基噻吩。后一反应也可应用于相应的噻唑、呋喃和恶唑类羧胺。并对上述产物的光学性质进行了测定。具有相当大的分子扭转的双噻吩衍生物显示出超过40%的荧光量子产率，这是非常有趣的。在进行这项工作的过程中，还开发了一些其他独特的芳基化反应。它们的应用将进一步研究。

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.