Regioselective Substitution of Heteroaromatic Compounds by Homogeneous Catalysis

已知杂芳族化合物的各种衍生物表现出药理活性。芳基取代的杂芳族化合物不仅作为药物，而且作为π共轭功能材料如荧光染料和有机半导体具有重要意义。因此，开发新的、有效的方法将芳基取代基引入到杂芳环中是一个重要的课题。本项目的目标是开发更通用、更有效的钯催化芳杂环直接芳基化反应的新方法，发现大体积的叔膦能有效地促进噻吩和噻唑在2-和5-位的反应。在某些情况下，铜（I）物质充当有效的助催化剂。在3-位上具有吸电子基团的噻吩不仅在2-位和5-位发生芳基化反应，而且在4-位也发生芳基化反应，得到三芳基噻吩衍生物。此外，发现2-噻吩甲酰胺经历三芳基化伴随脱氨甲酰化以产生2，3，5-三芳基噻吩。后一反应也可用于噻唑、呋喃和恶唑的相应羧酰胺。还测量了上述产物的光学性质。具有相当大的分子扭转的联噻吩衍生物显示出大于40%的荧光量子产率是非常令人感兴趣的。在进行本工作的过程中，还发展了一些独特的芳基化反应。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.