噻吩螺烯的化学与光化学合成

Chemical and Photochemical Synthesis of Thiophene-based Helicenes

本文综述了近年来噻吩螺烯的化学与光化学合成方面的重要进展。在螺烯的化学合成方面,阐明了单螺烯的常见合成手法,即以并三噻吩为构筑模块,合成螺烯前驱体联并三噻吩,其后通过硫代关环手法制备噻吩单螺烯。由于前驱体的两个并噻吩片段可能存在分子内的相互作用,造成无法无限制增长螺烯分子的尺寸。通过增加助溶基团的合成策略可以将螺烯的分子结构由单螺烯引入到双螺烯。在螺烯的光化学合成方面,光化学氧化关环的实例表明了光化学是构筑单螺烯与双螺烯的有效手法。由于存在前驱体双键在光照条件下可以打开产生双自由基的光化学反应机理,在其后关环步骤可有效产生外消旋体与内消旋体这样有趣的双螺烯产物。此外,本文针对噻吩螺烯领域的前景,提出了3个方面的观点:1)通过设计末端噻吩环上硫原子的位置异构,形成新的螺烯同分异构体;2)通过合成设计,可以制备新结构的双螺烯与多螺烯;3)通过手性拆分,可将螺烯旋光体应用于手性催化、手性组装等应用领域。

In this review,the main progresses on the chemical and photochemical synthesis of thiophene-based helicenes are described.In the section of chemical method for synthesis of helicenes,based on ditheinothiophene（DTT）as building blocks,the single helicenes are normally designed and synthesized to make bi-DTTas precursor first,and then implement sulfur substituted cyclization for target helicenes.However,it may not be successful for making longer and longer helicenes due to the increasing intramolecular interactions between the two moieties of precursor molecule.By the synthetic strategy of increasing the solubilizing groups in making helicenes,the target molecular structures can be changed from single helicenes to double helicenes.In the section of photochemical synthesis of helicenes,the oxidative photocyclization is confirmed to be an effective method for preparation of helicenes.Due to the double radical mechanism in the photochemistry of double bond under irradiation,the cyclization step gives the effective target products including both racemate and mesomer at the same time.In addition,the prospects for the field of thiophene-based helicenes are put forward in three aspects：1）design the new isomers of helicenes based on the position isomerism of sulfur atoms in the terminal thiophene rings of helicene;2）design and synthesis of double or multiple helicenes with new structures;3）find the application of helicene enantiomers in asymmetric catalysis,chiral assembly and so on.