Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany.
Chemistry. 2011 Oct 10;17(42):11838-43. doi: 10.1002/chem.201101739. Epub 2011 Sep 6.
Herein, we describe our attempts to systematically prepare a series of oligo(2-thienyl)-substituted pyridine derivatives. The crucial starting material, a β-alkoxy-β-ketoenamide, is easily available on a large scale by the reaction of lithiated methoxyallene with thiophene-2-carbonitrile and thiophene-2-carboxylic acid. This three-component reaction is followed by intramolecular cyclization to yield the suitably functionalized 2,6-di(2-thienyl)-substituted pyridine derivates. The two oxygen atoms allow the programmed activation of positions C-3, C-4, or C-5 of the pyridine ring to perform palladium-catalyzed coupling reactions with thiophene-2-boronic acid or 2-(tributylstannyl)thiophene, and alternatively, reductive removal of groups. With this concept, we were able to prepare five pyridine derivatives with 2-thienyl substituents in the 2,6-, 2,3,6-, 2,4,6-, 2,3,4,6-, and 2,3,5,6-positions. 2,3,4,5,6-Penta(2-thienyl)pyridine was not available with our methods. The UV/Vis and fluorescence spectra of all pyridines were recorded and showed a dependence on the substitution pattern and protonation state. For the protonated 2,3,5,6-tetra(2-thienyl)-substituted pyridine, a Stokes shift of about 180 nm with an emission at 515 nm was observed.
在此，我们描述了我们系统地制备一系列寡（2-噻吩基）取代吡啶衍生物的尝试。关键的起始原料，β-烷氧基-β-酮酰胺，通过锂化甲氧基烯丙基与噻吩-2-腈和噻吩-2-羧酸反应，很容易大规模获得。该三组分反应后进行分子内环化，得到适当官能化的 2,6-二（2-噻吩基）取代吡啶衍生物。两个氧原子允许对吡啶环的 C-3、C-4 或 C-5 位置进行程序激活，以进行钯催化的与噻吩-2-硼酸或 2-（三丁基锡基）噻吩的偶联反应，或者选择性地进行基团还原去除。基于此概念，我们能够制备 5 种具有 2-噻吩基取代基的吡啶衍生物，取代基位于 2,6-、2,3,6-、2,4,6-、2,3,4,6-和 2,3,5,6-位。我们的方法无法制备 2,3,4,5,6-五（2-噻吩基）吡啶。所有吡啶的 UV/Vis 和荧光光谱均已记录，并显示出对取代模式和质子化状态的依赖性。对于质子化的 2,3,5,6-四（2-噻吩基）取代吡啶，观察到约 180nm 的斯托克斯位移，发射波长为 515nm。
