The functionalized, enantiomerically pure [7]helicene 1 derived from bis(benzodithiophene) functionalized with four heptyl groups is prepared from 1,8-dibromo-4,5-diheptylbenzo[1,2-b:4,3-b']dithiophene building block 2. Such [7]helicene structure, functionalized with bromines at the terminal positions of the helicene inner rim and multiple solubilizing alkyl groups, is an attractive building block for long [n]helicenes and oligo[7]helicenes. Chirooptical properties and the degree of electron delocalization are determined and compared to those of analogous carbon-sulfur [7]helicene and [7]helicenes derived from benzodithiophene to provide a correlation between chirooptical properties and the degree of electron delocalization. [7]Helicene 1 possesses a moderately increased electron delocalization, but its chirooptical properties are similar to those for analogous [7]helicenes with relatively lower electron delocalization, indicating that chirooptical properties are not significantly affected by electron delocalization for this series of [7]helicenes. Molecular structures of racemic [7]helicene 1 and its benzodithiophene building block 2 are confirmed by single-crystal X-ray analysis. Crystals of 2 are chiral and adopt the shape of long, flexible, flat needles that can be readily bent.
Annelated Heptathiophene: A Fragment of a Carbon–Sulfur Helix
alpha-positions of thiophenes. Asymmetric synthesis is carried out using (-)-sparteine-mediated annelation of the axially chiral bis(aryllithium) with electrophilic sulfur equivalent. Alternatively, enantiomers of the [7]helicene are obtained via resolution using menthol-based chiral siloxanes. Racemic [7]helicene and four other macrocyclic products of the annelation are characterized by X-ray crystallography
描述了一种新型低聚噻吩的合成和表征,其中噻吩环退火成具有交叉共轭 pi 系统的 [7] 螺旋。这种 [7] 螺旋可以被视为前所未有的碳硫 (C(2)S)(n)() 螺旋的碎片,拥有富含硫的分子外围。[7] helicene 的外消旋合成基于两个步骤的迭代交替:噻吩的 β 位之间的 CC 键同源偶联和噻吩的 α 位之间的退火。使用 (-)-sparteine 介导的轴向手性双(芳基锂)与亲电子硫等价物的退火进行不对称合成。或者,[7]螺旋烯的对映异构体通过使用基于薄荷醇的手性硅氧烷拆分获得。外消旋 [7] helicene 和退火的其他四种大环产物通过 X 射线晶体学表征。[7] helicene 的一种溶剂多晶型物具有相反对映异构体的 pi 堆积柱和多个短分子间接触,包括同手性和异手性短 S...S 接触,表明在二维中存在有效的分子间电子耦合。[7]螺旋烯在室温下构型稳定,在 199 摄氏度时外消旋,半衰期约为