作者:Vít Lellek、Ivan Stibor
DOI:10.1039/a907825h
日期:——
We have designed and successfully synthesised dendrimers with axially chiral units in the interior structure. Starting from chiral 2,2′-dimethoxy-1,1′-binaphthalene building blocks 2 and 4 and from the four-directional initiator cores 7 and 8 the dendritic homochiral and heterochiral oligomers 9–16 were prepared. Using the [ϕ]D and Δε values of monomers 2 and 4, we calculated [ϕ]D and Δε values for dendrons 11, 13, and dendrimers 9, 10, 15 and 16. Although the observed molar optical rotation [ϕ]D of the dendrimers agrees relatively well with the calculated values, the CD measurements of all the dendrimers in THF and CH2Cl2, except that of heterochiral dendrimer 16 in THF, were significantly different from the calculated values. The intensive hypochromism of the dendrimers (between 37–59% in THF) and the agreement between the calculated and observed Δε values of the dendrons (between 14 and 6% in THF) led to the assumption that the hypochromic effect is caused by intramolecular interactions. From the NMR measurements it was proved that in the homochiral dendrimer 15, the N–H groups of the amides can form intramolecular hydrogen bonds that in CHCl3, with the help of the axially chiral moieties, cause a different conformation of the molecule than in the diastereomeric dendrimer 16.
我们设计并成功合成了具有轴向手性单元的树枝状聚合物。以手性 2,2′-二甲氧基-1,1′-联萘构件 2 和 4,以及四向引发剂核心 7 和 8 为起点,合成了树枝状同手性和异手性低聚物 9–16。利用单体 2 和 4 的 [ϕ]D 和 Δε 值,我们计算了树枝 11、13 以及树枝状聚合物 9、10、15 和 16 的 [ϕ]D 和 Δε 值。尽管观测到的树枝状聚合物的摩尔光学旋光度 [ϕ]D 与计算值相对一致,但在 THF 和 CH2Cl2 中测得的所有树枝状聚合物的 CD 值(除了在 THF 中的异手性树枝状聚合物 16)与计算值显著不同。树枝状聚合物的强烈减色现象(在 THF 中介于 37–59%)以及树枝的计算与观测 Δε 值一致(在 THF 中介于 14 和 6%)使我们假设减色效应是由分子内相互作用引起的。通过 NMR 测量证明,在同手性树枝状聚合物 15 中,酰胺的 N–H 基团可以形成分子内氢键,在 CHCl3 中,借助于轴向手性基团,导致分子与非对映体树枝状聚合物 16 具有不同的构象。