作者:Geir Kildahl-Andersen、Thorleif Anthonsen、Synnøve Liaaen-Jensen
DOI:10.1039/b706212e
日期:——
The carotene-like polyenes decapreno-β-carotene (C50), C54-β-carotene (C54, first synthesis) and dodecapreno-β-carotene (C60) with 15, 17 and 19 conjugated double bonds, respectively, were synthesized by double Wittig reactions. Introduction of a leaving group in allylic position failed, and cations were obtained by hydride elimination effected by i) triphenylcarbenium tetrafluoroborate-d15, prepared by a new method, or ii) treatment with trifluoroacetic acid-d. Deuterated reagents were employed for product analysis by 1H NMR. Parallel experiments were performed with β,β-carotene (C40). NIR spectra at room temperature and at –15 °C were employed for characterisation and stability studies of the cationic products. In CH2Cl2λmax in the 900–1350 nm region was recorded. NMR data for the cationic product of β,β-carotene obtained by the two new preparation methods were consistent with the two monocations previously characterised. The cationic products of the longer polyenes provided downfield-shifted, broadened signals, compatible with C50-monocation, mixed C54-mono- and dication and C60-dication. Combined NIR and NMR data suggest that the extent of charge delocalisation is limited by the maximum soliton width for cations obtained from linear polyenes with more than ca. 20 sp2-hybridized carbon atoms.
合成了类胡萝卜素多烯物质:十环烯-β-胡萝卜素(C50)、C54-β-胡萝卜素(C54,首次合成)和十二环烯-β-胡萝卜素(C60),它们分别具有15、17和19个共轭双键,采用双威提反应合成。未能在烯丙位引入离去基团,通过氢离子消除反应获得了阳离子,该反应由以下两种方法实现:i)通过一种新方法制备的三苯基卡宾四氟硼酸盐-d15,或ii)用三氟醋酸-d处理。采用氘代试剂进行产物分析,使用1H NMR进行表征。与β,β-胡萝卜素(C40)进行了平行实验。使用室温和-15°C的近红外光谱(NIR)对阳离子产物进行了特征化和稳定性研究。在CH2Cl2中记录了900–1350 nm波段的最大波长。通过两种新制备方法获得的β,β-胡萝卜素阳离子产物的NMR数据与先前表征的两个单阳离子一致。较长多烯的阳离子产物提供了向下偏移和宽化的信号,与C50单阳离子、混合C54单阳离子和双阳离子以及C60双阳离子相兼容。综合NIR和NMR数据表明,由于大约20个sp2杂化碳原子的线性多烯产生的阳离子的电荷离域程度受到最大孤子宽度的限制。