Ethynyl π-extended 2,5-diphenyl-1,3,4-oxadiazoles and 2-phenyl 5-(2-thienyl)-1,3,4-oxadiazoles: synthesis, X-ray crystal structures and optical properties
作者:Gregory Hughes、David Kreher、Changsheng Wang、Andrei S. Batsanov、Martin R. Bryce
DOI:10.1039/b407698m
日期:——
2-(4-tert-Butylphenyl)-5-(4-ethynylphenyl)-1,3,4-oxadiazole 1 reacts with a series of heteroaryl iodides under standard Sonogashira cross-coupling conditions (Pd[PPh3]2Cl2, CuI, triethylamine, THF) to yield products 2aâg in 40â79% yields (heteroaryl = 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrazyl, 5-bromo-2-pyrimidyl, 2-thienyl and 3-thienyl, respectively). Compound 2f was lithiated followed by electrophilic iodination (BuLi, perfluorohexyl iodide) to give 3, which by a two-step sequence gave the terminal ethynylthienyl derivative 5. Conversion of 5 into the terminal ethynylaldehyde derivative 7, via acetal derivative 6, proceeded in high yield. Starting from 2-iodo-5-methoxycarbonylthiophene, a five-step sequence afforded 2-(4-tert-butylphenyl)-5-(4-ethynylthienyl)-1,3,4-oxadiazole 13
(13% overall yield). Reactions of 13 gave terminal pyridyl, pyrazyl, pyrimidyl and thienyl derivatives, analogous to those obtained from 1. Two-fold reaction of 13 with 2,5-diiodothiophene gave the bis(ethynylthienyl)thiophene derivative 15
(30% yield). Solution UV-Vis absorption and photoluminescence spectra establish that replacement of the phenyl ring in the 2,5-diphenyl-1,3,4-oxadiazole series 2aâg by a thienyl ring [i.e. the 2-phenyl-5-(2-thienyl)-1,3,4-oxadiazole series 14aâg] leads to a red shift in the lowest energy band in both the absorption spectra and emission spectra. The X-ray crystal structures of compounds 2d, 2g, 5 and 14d·CHCl3 reveal that the molecular structures are approximately planar although there are substantial differences in the conformations.
2-(4-叔丁基苯基)-5-(4-乙炔基苯基)-1,3,4-噁二唑1在标准Sonogashira交叉偶联条件下(Pd[PPh3]2Cl2,CuI,三乙胺,THF)与一系列杂环碘化物反应,生成产物2a–g,产率为40–79%(杂环分别为2-吡啶基、3-吡啶基、4-吡啶基、2-吡唑基、5-溴-2-嘧啶基、2-噻吩基和3-噻吩基)。化合物2f经锂化后再进行亲电碘化(BuLi,全氟己基碘)得到3,通过两步序列得到末端乙炔基噻吩衍生物5。将5转化为末端乙炔基醛衍生物7,经过缩醛衍生物6,过程产率高。从2-碘-5-甲氧羰基噻吩出发,经过五步合成得到2-(4-叔丁基苯基)-5-(4-乙炔基噻吩基)-1,3,4-噁二唑13(总产率13%)。13的反应得到了类似于1的末端吡啶基、吡唑基、嘧啶基和噻吩基衍生物。13与2,5-二碘噻吩的双重反应得到双(乙炔基噻吩基)噻吩衍生物15(产率30%)。溶液UV-Vis吸收光谱和光致发光光谱表明,将2,5-二苯基-1,3,4-噁二唑系列2a–g中的苯环替换为噻吩环(即2-苯基-5-(2-噻吩基)-1,3,4-噁二唑系列14a–g)导致吸收光谱和发射光谱中的最低能量带发生红移。化合物2d、2g、5和14d·CHCl3的X射线晶体结构揭示,尽管构象存在较大差异,分子结构大体上是平面型的。