Rajca Andrzej, Miyasaka Makoto, Pink Maren, Wang Hua, Rajca Suchada
Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588-0304, USA.
J Am Chem Soc. 2004 Nov 24;126(46):15211-22. doi: 10.1021/ja0462530.
The synthesis and characterization of a novel oligothiophene, in which the thiophene rings are annelated into a [7]helicene with cross-conjugated pi-system, are described. Such [7]helicenes may be viewed as fragments of the unprecedented carbon-sulfur (C(2)S)(n)() helix, possessing sulfur-rich molecular periphery. Racemic synthesis of [7]helicene is based upon iterative alternation of two steps: C-C bond homocouplings between the beta-positions of thiophenes and annelation between the 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. One of the solvent polymorphs of the [7]helicene possesses pi-stacked columns of opposite enantiomers and multiple short intermolecular contacts, including both homochiral and heterochiral short S...S contacts, suggesting an effective intermolecular electronic coupling in two-dimensions. The [7]helicene is configurationally stable at room temperature and racemizes at 199 degrees C with a half-time of about 11 h. Selected physicochemical studies (UV-vis absorption, CD, optical rotation, and cyclic voltammetry) of the [7]helicene are described.
本文描述了一种新型低聚噻吩的合成与表征，其中噻吩环稠合形成具有交叉共轭π体系的[7]螺旋烯。这种[7]螺旋烯可被视为前所未有的碳 - 硫（C₂S）ₙ螺旋的片段，其分子外围富含硫。[7]螺旋烯的外消旋体合成基于两个步骤的迭代交替：噻吩β位之间的C - C键均偶联以及噻吩α位之间的稠合。不对称合成是通过（ - ） - 鹰爪豆碱介导的轴向手性双（芳基锂）与亲电硫等价物的稠合来进行的。或者，[7]螺旋烯的对映体通过使用基于薄荷醇的手性硅氧烷进行拆分获得。外消旋[7]螺旋烯和其他四种稠合大环产物通过X射线晶体学进行表征。[7]螺旋烯的一种溶剂多晶型物具有相反对映体的π堆积柱以及多个短分子间接触，包括同手性和异手性的短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℃外消旋，半衰期约为11小时。本文还描述了对[7]螺旋烯进行的选定物理化学研究（紫外 - 可见吸收、圆二色性、旋光性和循环伏安法）。
