Acta Chimica Sinica ›› 2022, Vol. 80 ›› Issue (1): 29-36.DOI: 10.6023/A21110508 Previous Articles     Next Articles



段超a, 张建伟b, 向焌钧a, 杨笑迪b,*(), 高希珂a,*()   

  1. a中国科学院大学 中国科学院上海有机化学研究所 中国科学院有机功能分子合成与组装化学重点实验室 上海 200032
    b上海中医药大学 创新中药研究院 上海 201203
  • 投稿日期:2021-11-09 发布日期:2021-12-08
  • 通讯作者: 杨笑迪, 高希珂
  • 作者简介:
  • 基金资助:
    项目受国家自然科学基金(21790362); 项目受国家自然科学基金(22075310); 上海市科学技术委员会项目(19XD1424700); 上海市科学技术委员会项目(18JC1410600)

Design, Synthesis and Properties of Azulene-Based BN-[4]Helicenes

Chao Duana, Jianwei Zhangb, Junjun Xianga, Xiaodi Yangb(), Xike Gaoa()   

  1. aKey Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032, China
    bInnovation Research Institute of Traditional Chinese Medicine, Shanghai University of Traditional Chinese Medicine, Shanghai 201203, China
  • Received:2021-11-09 Published:2021-12-08
  • Contact: Xiaodi Yang, Xike Gao
  • About author:
    Dedicated to the 10th anniversary of the Youth Innovation Promotion Association, CAS.
  • Supported by:
    National Natural Science Foundation of China(21790362); National Natural Science Foundation of China(22075310); Science and Technology Commission of Shanghai Municipality(19XD1424700); Science and Technology Commission of Shanghai Municipality(18JC1410600)

Azulene is a nonalternant and nonbenzenoid hydrocarbon with bright blue color and a dipole moment of 1.08 D, and has received increasing attention due to its unique electronic structure and physicochemical properties. Herein, we report the design and synthesis of two types of azulene-based [4]helicene 1a/1b and 2 that contain isoelectronic B—N and C=C units at the electron-rich 1-position of azulene unit, respectively. Formation of the helical scaffolds is executed by the introduction of boron and alkyne to flexible biaryl precursors, where the Lewis acidic boron and alkyne were employed as “glue” to join two subunits into fully fused scaffolds via electrophilic boronation and platinum-catalyzed cycloisomerization of alkyne at the 1-position of azulene unit, respectively. All of azulene-based helicenes were investigated by ultraviolet visible (UV-vis) absorption spectra, cyclic voltammetry (CV) measurements and density functional theory (DFT) calculations. Additionally, 1a was further characterized by single crystal structure analysis. The results suggest that the introduction of B—N unit changed the electronic structure of the conjugated aromatic framework, leading to a narrow HOMO-LUMO gap. Moreover, the B—N unit also affects the aromaticity of the π-system as revealed by nucleus-independent chemical shift (NICS) via time-dependent density functional theory (TD-DFT) calculation. The single crystal structure analysis demonstrates that 1a has a helically twisted framework and Plus (P)/Minus (M) enantiomers. However, the Gibbs activation energy (ΔG(T)) of the enantiomerization at room temperature is too low to separate two enantiomers by chiral high performance liquid chromatography (HPLC). Furthermore, the B—N unit exhibits partial double bond character and the BN-containing six-membered ring shows weak aromaticity. 1a with a phenyl group exhibits the deboronization upon addition of trifluoroacetic acid (TFA) as well as a specific sensing behavior to fluoride ion. However, 1b shows no deboronization upon addition of TFA and no sensing behavior to fluoride ion due to its steric hindered mesityl (Mes) group, but has a reversible stimuli-responsiveness with acid and base, this proton-responsiveness is similar to all-carbon analogue 2.

Key words: azulene, BN-heteroaromatic, helicene, protonation