Rational synthesis of meso-substituted chlorin building blocks
Rational synthesis of meso-substituted chlorin building blocks
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DOI：
10.1021/jo991942t
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发表时间：
2000-05-19
影响因子：
3.6
通讯作者：
Lindsey, JS
中科院分区：
文献类型：
--
作者：
Strachan, JP;O'Shea, DF;Lindsey, JS
氯素为植物光合作用提供了基础，但由于缺乏合适的氯素构件，合成模型系统通常使用卟啉作为替代品。我们采用了一条由Battersby开创的路线，以获得带有两个中位取代基的氯素，一个双子二甲基团来锁定氯素的氢化水平，并且没有侧翼的中位取代基和β取代基。综合包括东半部和西半部的汇合。以吡咯-2-甲醛为原料，经四步反应合成了3，3-二甲基-2，3-二氢二氢吡咯(Western Half)。以5-取代二吡咯甲烷为原料，经酰化、溴化、还原反应制得溴代吡咯甲烷甲醇(东半部)。二氯的形成是通过酸催化缩合和金属介导的氧化环合的两个烧瓶过程实现的。到目前为止，后一反应是用铜模板进行的。对这种多步骤工艺条件的研究导致了无铜条件(醋酸锌、AgIO3和哌啶在甲苯中在80℃下反应2小时)。氯化锌的产率接近10%，并且可以很容易地脱金属得到相应的游离碱氯。该合成方法与一系列中间取代基(对甲苯基、甲苯基、五氟苯基、4-[2-(三甲基硅基)乙炔基]苯基、4-碘苯基)相容。共制备了四个游离碱和四个氯化锌。氯素表现出典型的吸收光谱、荧光光谱和荧光量子产率。这些类型的氯素易于合成，存在合适的取代基，并且具有特有的光谱特征，因此非常适合用于合成模型体系。
Chlorins provide the basis for plant photosynthesis, but synthetic model systems have generally employed porphyrins as surrogates due to the unavailability of suitable chlorin building blocks. We have adapted a route pioneered by Battersby to gain access to chlorins that bear two meso substituents, a geminal dimethyl group to lock in the chlorin hydrogenation level, and no flanking meso and beta substituents. The synthesis involves convergent joining of an Eastern half and a Western half. A 3,3-dimethyl-2,3-dihydrodipyrrin (Western half) was synthesized in four steps from pyrrole-2-carboxaldehyde. A bromodipyrromethane carbinol (Eastern half) was prepared by sequential acylation and bromination of a 5-substituted dipyrromethane followed by reduction. Chlorin formation is achieved by a two-flask process of acid-catalyzed condensation followed by metal-mediated oxidative cyclization. The latter reaction has heretofore been performed with copper templates. Investigation of conditions for this multistep process led to copper-free conditions (zinc acetate, AgIO3, and piperidine in toluene at 80 degrees C for 2 h). The zinc chlorin was obtained in yields of similar to 10% and could be easily demetalated to give the corresponding free base chlorin. The synthetic process is compatible with a range of meso substituents (p-tolyl, mesityl, pentafluorophenyl, 4-[2-(trimethylsilyl)ethynyl]phenyl, 4-iodophenyl). Altogether four free base and four zinc chlorine have been prepared. The chlorins exhibit typical absorption spectra, fluorescence spectra, and fluorescence quantum yields. The ease of synthetic access, presence of appropriate substituents, and characteristic spectral features make these types of chlorins well suited for incorporation in synthetic model systems.