Meier H, Lehmann M, Kolb U
Institut fur Organische Chemie, Johannes Gutenberg-Universitat, Mainz, Germany.
Chemistry. 2000 Jul 3;6(13):2462-9. doi: 10.1002/1521-3765(20000703)6:13<2462::aid-chem2462>3.0.co;2-a.
The first five generations of the stilbenoid dendrimers 1(n) (n = 1-5) have been prepared by a combined coupled synthesis (between the generations of the dendrons 8-12) and convergent synthesis. Wittig-Horner reactions together with a protecting group technique yield monodisperse compounds of high constitutional and configurational purity. The solubility of the stiff molecules, which have primarily a disklike shape in the first and second generations and a cylindrical shape in the third, fourth, and fifth generations, is governed by the alkoxy chains that are attached to the peripheral benzene rings. The number of stilbene building blocks increases according to the formula 3(2(n)-1) from 3 in the first generation (n = 1) to 93 in the fifth generation (n = 5). Consequently, the molecular mass reaches 24,000 in 1(5)b which contains 144 hexyloxy chains. An exact measurement of the mass is provided by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. In solution, the stilbenoid dendrimers 1(n) exhibit a strong tendency to aggregate, which increases from generation to generation. In the pure state, columnar mesophases Col(hd) (1(1)b, 1(1)c, 1(2)b, and 1(2)c) and Col(ob) (1(2)b, 1(2)c) are formed; intramolecular steric hindrance prevents such ordered arrangements in higher generations 1(n) (n = 3, 4, 5).
通过树枝状分子8-12各代之间的偶联合成与收敛合成相结合的方法，制备了前五代芪类树枝状大分子1(n)（n = 1-5）。Wittig-Horner反应与保护基技术相结合，得到了具有高结构和构型纯度的单分散化合物。这些刚性分子在第一代和第二代主要呈盘状，在第三代、第四代和第五代呈圆柱状，其溶解性由连接在外围苯环上的烷氧基链决定。芪结构单元的数量按照公式3(2(n)-1)增加，从第一代（n = 1）的3个增加到第五代（n = 5）的93个。因此，在含有144条己氧基链的1(5)b中，分子量达到24,000。基质辅助激光解吸电离飞行时间（MALDI-TOF）质谱提供了精确的分子量测量。在溶液中，芪类树枝状大分子1(n)表现出强烈的聚集倾向，且这种倾向代代增加。在纯态下，形成了柱状中间相Col(hd)（1(1)b, 1(1)c, 1(2)b,和1(2)c）和Col(ob)（1(2)b, 1(2)c）；分子内空间位阻阻止了更高代1(n)（n = 3, 4, 5）形成这种有序排列。
