Study On The Synthesis Of Dithienoheteroaromatic Rings And [5] Helicene

Due to the favorable optical and electrical properties, derivatives ofdithienoheteroaromatic rings （DTHAs） have greatly potential application in organic fieldeffect transistors （OFETs）, organic light emitting diodes （OLEDs） and organic solar cells（OSCs）. In this thesis, the efficient and simple synthesis of symmetrical and unsymmetricalDTHAs has been developed via intramolecular cyclization of4,4’-dibromo-3,3’-bithiophene（7）. In addition, we found a novel synthetic route to [5]Helicene, and we synthesized somederivatives of3-bromo-dithieno [2,3-b:3’,4’-d]thiophene （1）.The research work in this dissertation is composed of three parts:Part I. Study on synthesis of dithienoheteroaromatic ringsIt is known that the reactivity of n-BuLi depends on its aggregation types, and thesolvent systems will greatly influence aggregation types and the reactivity of n-BuLi. With thereactivity difference of n-BuLi, it will influence the selectivity of the Br/Li exchange（including mono and double Br/Li exchanges） and deprotonation and further determine thefinal components of the products. With7as starting material, in the presence of n-BuLi/Et₂O,the Br/Li exchange and deprotonation reactions took place at the same time, followed byaddition of three electrophilic reagents （22a-22c）, and the corresponding unsymmetricalDTHAs （1-3） were obtained with efficient yields （57.3%,56.0%, and58.6%for1,2, and3,respectively）. And meanwhile, there were a small amounts of the corresponding symmetricalDTHAs （4-6）（11.3%,9.6%, and9.0%for4,5, and6, respectively） were generated. In thecase of n-BuLi/THF、s-BuLi/Et₂O or t-BuLi/Et₂O, no unsymmetrical DTHAs was observed,and only the symmetrical ones （4-6） were generated. Compounds1-6were confirmed by¹HNMR,¹³C NMR, MS and IR, compounds1-3were also confirmed by HRMS, and both1and 2were confirmed by X-ray crystallographic analysis. We also proposed the possiblemechanism for the formation of symmetrical and unsymmetrical DTHAs in the reactions.PartⅡ. Study on the synthesis of [5]Helicene （18）So far, all the S atoms in the reported [5]Helicene were arrayed outwards, i.e. all thethiophene rings were arranged in just the same way. We expected that new [5]Helicene couldbe synthesized via the forming mechanism of Br-bs-DTHAs addressed in the Part I, i.e. bothBr/Li exchange and deprotonation of7took place at the same time in the presence ofn-BuLi/Et₂O. In this part, Negishi coupling reaction was employed to form importantprecursor14.[5]Helicene （18） was designed to be synthesized via Br/Li exchange anddeprotonation from compound14in one-pot in the presence of n-BuLi/Et₂O. However, theactual reaction didn’t work as we expected. Due to the low reactivity of the α-H on the fusedrings, when2equiv n-BuLi in Et₂O was utilized to react with compound14, only thethiobutyl compound16was obtained finally in39.3%yield. Finally, the synthetic route of theaim [5]Helicene （18） had to be corrected. Firstly, the dibromo compound15was efficientlysynthesized （yields89.4-95.5%） via introduceding-Br to the α position on fused rings of14in the case of LDA/BrCl2CCCl2Br. Then, t-BuLi was employed to react with compound15inEt₂O at-78oC, after quenched with the （PhSO2）2S, the final [5]Helicene （18） was obtained（yields:21.9-31.6%）. Compounds14-18were confirmed by¹H NMR,¹³C NMR, MS, HRMS,and IR. Compounds16-17were confirmed by X-ray crystallographic analysis.Part Ⅲ. Study on the synthesis of derivatives of dithieno[2,3-b:3’,4’-d]thiophene3-bromo-dithieno[2,3-b:3’,4’-d]-thiophene （1） could be applied as organic functionalmaterials due to the active positions on the thiophene rings, from which it may generate avariety of derivatives. In this part, several derivatives, which could be utilized as the crucialprecusers in the synthesis of the organic functional materials, were attempted to synthesizebased on the compund1. Since there were three approximatively active α-H in1, it is difficult to get the mono-substituted derivatives. In this part, with introduction of trimethylsilyl （TMS）groups as protecting and solubilizing groups to1,3-bromo-2,4,6-tris（trimethylsilyl）-dithieno-[2,3-b:3’,4’-d]thiophene （19） was obtained （yields:94.1-98.1%）. After experiencing in n-BuLi,when quenching with CuCl2,the coupling product2,2’,4,4’,6,6’-hexa（trimethylsilyl）-3,3’-bidithieno[2,3-b:3’,4’-d]thiophene （21） was obtained （yields:53-58%）. When DMF or H₂Owas utilized to quench the reactions, it was fascinating to find that3-butyl-2,4,6-tris（trimethylsilyl）dithieno-[2,3-b:3’,4’-d]thiophene （20） was generated.Compounds19-21were confirmed by¹H NMR,¹³C NMR, MS, HRMS, and IR.