Synthesis Of C₂-symmetric BINOL-based Heterocyclic Compounds And Oligomers

Organic electronics have attracted numerous attentions due to their potential applications that can provide low-cost, large-area electronic devices on arbitrary substrates. In this area, organic semiconductor materials have been developed significantly in the past decades. Among those plenty of molecular classes reported so far, ladder-type π-conjugated molecules often referred as acenes or heteroacenes have been investigated as promising organic semiconductors that turn out to have realized high-performance organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). Those progresses have been approached not only in small organic molecules but also in polymers. Primarily studied structures are benzothiophenes, furans and benzo-selenophenes. It is interesting to note that the electronical properties of thiophene are similar with those in selenophene, and are quite diffirent with those in furan. That is to say that furan core could be an interesting π-extended core for study.This prompts us to synthesiz a series of C2-symmetrical heterocyclic compounds and oligomers based on BINOL from well-defined synthetic routes. These combinations could arise from one or two furan or thiophene rings fused with binaphthyl motif to result into binaphtho[2,3-b]furan and dinaphtho[2,1-b:1’,2’-d]furan compounds.In the first part, we discussed the synthesis of chiral 9,9’-binaphtho[2,3-b]furan compounds and oligomers. Initially chiral 2,2’-dimethoxy-1,1’-binaphthalenes were obtained by the reaction of chiral BINOL and MeI in the presence of K2CO3. Then lithiation reactions were performed with BuLi and subsequently quenched with iodine to afford 2,2’-dimethoxy-3,3’-diiodine-1,1’-binaphthslene. Then deprotection was conducted with BBr3 in CH2Cl2 to afford 2,2’-dihydroxy-3,3’-diiodo-1,1’ binaphthalene. The acylation of hydroxyl groups were furnished with Ac2O in the presence of pyridine. The Sonogashira coupling reactions with five different alkynes by Pd(PPh3)2Cl2/CuI/Et3N system in DMF were employed to afford 3,3’-dialkynyl-2,2’-diacetoxy-1,1’-binaphthalenes. The final ring closure reactions were completed by Cs2CO3 to afford target compounds 9,9’-binaphtho[2,3-b]furans. Then 3,3’-bis(2-thienyl)-9,9’-binaphtho[2,3-b]furan was employed as one of the monomers to form some oligomers through newly developed Direct Arylation Polycondesation(DHAP), which was an economical and eco-friendly way for polymerization. We screened the polymerization conditions of the template reactions using 2,2’-bis(2-thienyl)-9,9’-binaphtho[2,3-b]furan and 2,7-dibromo-9-(2-ethylhexyl)-9H-carbazale as monomers. Then dibromomonomers such as 4,7-dibromobenzothiadiazole,4,4’-dibromobiphenyl, 5,9-dibromo-dinaphtho[2,1-b:1’,2’-d],2,7-dibromo-9-(2-ethylhexyl)-9H-carbazole and 3,6-dibromo-9-(2-ethylhexyl)-9H-carbazole were chosen to polumerize with 2,2’-bis(2-thienyl)-binaphtho[2,3-b]furan under opitimized condition. As a result, we obtained several oligomers with molecular weight (Mn,2,532 to 4,307) and polydispersity index (PDI,1.001-1.289), which showed quite high stereoregular degree. Parts of those oligomers with internal D-A structure might have the potential to be used in the field of low band-gap OP Vs.In the second part, we discussed the synthesis of dinaphtho[2,1-b:1’,2’-d]furan and dinaphtho[2,1-b:1’,2’-d]thiophene. (a) The dehydration of chiral BINOL in the presence of p-TsOH led to the formation of dinaphtho[2,1-b:1’,2’-d]furan, which was brominated with NBS to afford (S)-/(R)-5,9-dibromine-dinaphtho[2,1-b:l’,2’-d]furan. The product obtained above was then subsequently processed Suzuki cross coupling with eleven arylboronic acids cayalyzed by Pd-132 catalyst, which is air-and moisture-stable with lower catalystloading. (b) Firstly BINOL was pretreated with NaH and then reacted with dimethylcarbamothioic chloride.In order to obtain dinaphtho[2,1-b:l’,2’-d]thiophene, the product above was reacted under temperature as high as 275℃ for 40 min (Due to the rotation of the structure under such high temperature, we recoginized that the corresponding chirality was disappeared.). Subsequently dinaphtho[2,1-b:l’,2’-d]thiophene was brominated with Br2 to afford 5,9-dibromine-dinaphtho[2,1-b:1’,2’-d]thiophene, which was finally processed the same Suzuki cross coupling as described above with six arylboronic acids catalyzed by the same catalyst Pd-132 to obtain 5,9-diaryl-dinaphtho[2,1-b:1’,2’-d]thiophene.