Synthesis Of New Cyclooctatetrathiophenes Based On Bithiophene Dicarbanions And Synthetic Attempt Of New Thiophene-based [7]Helicene

Cyclooctatetraaryl compoundscontaining a cyclooctatetraene（COT）coreand four aromatic ringshave attracted more attentions in the field of optoelectronic materials.Among them,cyclooctatetrathiophenes（COTh）have received considerable interest since they have many isomers and more reactive sites.By using these sites,more derivatives can be synthesized.In this dissertation,new isomers of cyclooctatetrathiophene（COTh）withbothβ-βandα-βlinkingmodes,named2,4,6,8,10,12-hexaylhexakis（trimethylsilane）-cycloocta[1,2-b:5,6-b’:3,4-c’:7,8-c’’]tetrathiophene（COTh-1-（TMS）₅）,2,4,6,7,9,11-hexaylhexakis（trimethylsilane）-cycloocta[1,2-b:8,7-b’:3,4-c’:5,6-c’’]tetra-thiophene（COTh-2-（TMS）₅）and 2,5,7,9,11-pentaylpentakis（trimethylsilane）cycloocta[1,2-b:3,4-b’:8,7-b’:5,6-c’’]tetrathiophene（COTh-3-（TMS）₅）,are designed and synthesized based on the synthetic strategy of bithiophene dicarbanions and the physical properties of these three COThs werestudied.In addition,the same method was applied to explore the synthesis of the new thiophene-based[7]helicene（16）.The main work of the dissertation can be divided into the following three parts:I.The synthesis ofthree new cyclooctatetrathiophenesStarting from 3,4-dibromothiophene-2,5-bis（trimethyl）thiophene and 2-trimethyl-4-（4,4,5,5-tetramethyl-1,3,2-dioxaborolan）thiophene,4-bromo-2,5,5’-tris（trimethylsilane）-3,3’-bithiophene（4）could be synthesized via Suzuki coupling in a yield of 40%.Li/Br exchange and deprotonation of 4 were proceed in one-pot in the presence of n-BuLi and the bithiophene dicarbanion was used directly without any treatmentfor the next step.When bithiophene dicarbanion was treated with CuCl₂,then COTh-1-（TMS）₆and COTh-2-（TMS）₆were prepared by intermolecular cyclization in one pot in yiels of 20%and22%,respectively.Simlarly,2’,4-diiodo-2,5,5’-tris（trimethylsilane）-3,3’-bithiophene（5）was synthesized in the yield of 62%by the quenching reaction of iodine.When 5 was treated withorganic zinc intermediate,2’’,5,5’,5’’,5’’’-pentaylpentakis（trimethylsilane）-3,2’:3’,3’’:4’’,3’’’-quaterthiophene（6）could be generated in a yield of 34%.Finally,COTh-3-（TMS）₅could be prepared via the selective deprotonation of 6and the following intramolecular cyclization in the presence of n-BuLi and CuCl₂.The total yields of COTh-1-（TMS）₆,COTh-2-（TMS）₆and COTh-3-（TMS）₅were 5.5%,6.0%and 3.1%,respectively.The three COThsand all intermediate compounds were characterized by ¹H NMR,¹³C NMR,HRMS and IR.At the same time,molecular structures of the three COThswere characterized by X-ray crystal analysis,which indicates the structural characteristics ofthe"saddle"skeletons.II.Physical properties of the three new cyclooctatetrathiophenesThe UV-vis absorption spectra and electrochemistry properties of the three new COThswere characterized.Through the UV-vis spectra of COTh-1-（TMS）₆,COTh-2-（TMS）₆and COTh-3-（TMS）_5,it’s clear thatthree COThs presented differentabsorption curves.COTh-1-（TMS）₆has two absorption bands which arelocated at 220-260 nm（band I）and 260-330 nm（band II）.COTh-2-（TMS）₆displayedthree absorption bands which arelocated at 220-250 nm（band I）,250-290 nm（band II）and 290-350 nm（band III）.COTh-3-（TMS）₅alsoshowedthree absorption bands which arelocated at 220-250 nm（band I）,250-320nm（band II）and 320-380 nm（band III）.By comparing the maximum long-wave absorption of the three COThs,itindicatesthattheconjugationdegreeisCOTh-3-（TMS）5>COTh-2-（TMS）6>COTh-1-（TMS）6,which may be influenced by the single-double bond distribution in the COTh rings and steric hindrance induced by the TMS groups.In addition,the NICS calculation was also performed andCOTh-3-（TMS）₅bears the biggest anti-aromatic value.Cyclic voltammetry（CV）is also carried out for the three COTh molecules and the results revealedthat the first oxidation potentials（versus Fc/Fc⁺）ofCOTh-1-（TMS）₆、COTh-2-（TMS）₆and COTh-3-（TMS）₅are1.09 V,0.91 V and 1.02 V,respectively,indicating good redox stability.Ⅲ.The synthetic attempt of new thiophene-based[7]heliceneBased on the bithiophene dicarbanions synthetic strategy,2-bromo-4,6-bis（trimethylsilane）-dithieno[2,3-b:3’,4’-d]thiophene（12）can be generated anda new thiophene-based[7]helicene（16）has been designed and tried to synthesis.Starting from 4,5-dibromo-2-trimethylsilane-thiophene（1）,compound 12can be synthesized with a yield of 10.7%via Suzuki cross coupling reaction,double anionizationundern-BuLi,intramolecular cyclization reaction under（PhSO₂）₂S,deprotonation undern-BuLi and bromination reaction under 1,2-dibromotetrachloroethane.Subsequently,compound 12was reacted with n-BuLiandquenchedwith（PhSO₂）₂Ssuccessivelytoformthe bis（4,6-bis（trimethylsilyl）dithieno[2,3-b:3’,4’-d]thiophen-2-yl）sulfane（13）with a yield of 52%.But the final removal of theβ-proton of compound 13was failed and the target compound16was not obtained.All intermediates were confirmed by ¹H NMR,¹³C NMR and HRMS and compound 13was confirmed by single-crystal X-ray analysis.Although the new thiophene-based[7]helicene was not successfully obtained,a variety of intermediate products are obtained in high yields,which are important building blocks for organic functional materials.