Wagner Carl E, Kim Jang-Seob, Shea Kenneth J
Department of Chemistry, University of California Irvine, Irvine, California 92697, USA.
J Am Chem Soc. 2003 Oct 8;125(40):12179-95. doi: 10.1021/ja0361291.
Trialkyl and triaryl organoboranes undergo multiple, repetitive homologations upon reaction with dimethylsulfoxonium methylide (1). This multiple homologation reaction, or polyhomologation, produces polymethylene in a living reaction. Applying the polyhomologation reaction to cyclic and polycyclic organoboranes permits the construction of unique oligomeric and polymeric architectures that are not readily accessible by standard olefin polymerization. The polyhomologation of 1-boraadamantane.THF (2) by ylide 1 generates novel macrotricyclic trialkylboranes (3). The oxidation of these macrocyclic organoboranes generates a three-armed star polymethylene polymer (4) incorporating a cis,cis-1,3,5-trisubstituted cyclohexane core. Interestingly, only one-third of the initiators lead to product formation, resulting in an observed degree of polymerization 3 times higher than expected. Close examination of the initial stages of polymerization show that 1-boraadamantane.THF reacts with 1 equiv of 1 to afford a monohomologated product. Subsequent homologations were found to contain branch points leading to isomeric tricyclic products after the third, fourth, and fifth methylene insertions. At these stages of homologation, all of the propagating species result in tricyclic trialkylborane cages with collapsed, inverted pyramidal boron centers that are substantially less reactive toward ylide. Approximately two-thirds of the species discontinue polymerization at these stages. However, one-third of these species continue to propagate and eventually result in the formation of giant macrotricyclic polymers of narrow polydispersity. Molecular modeling and kinetic simulation have aided in the analysis of the probable pathways through which the reaction proceeds.
三烷基和三芳基有机硼烷与二甲基亚砜甲基叶立德（1）反应时会发生多次重复的同系化反应。这种多次同系化反应，即多同系化反应，在活性反应中生成聚亚甲基。将多同系化反应应用于环状和多环有机硼烷，可以构建独特的低聚和聚合结构，而这些结构通过标准烯烃聚合难以获得。1-硼金刚烷·四氢呋喃（2）与叶立德1发生多同系化反应生成新型的大环三环三烷基硼烷（3）。这些大环有机硼烷的氧化生成了一种包含顺式，顺式-1,3,5-三取代环己烷核心的三臂星形聚亚甲基聚合物（4）。有趣的是，只有三分之一的引发剂导致产物形成，导致观察到的聚合度比预期高3倍。对聚合初始阶段的仔细研究表明，1-硼金刚烷·四氢呋喃与1当量的1反应生成单同系化产物。随后的同系化反应发现含有分支点，在第三次、第四次和第五次亚甲基插入后导致生成异构的三环产物。在这些同系化阶段，所有增长物种都会生成具有塌陷的倒金字塔形硼中心的三环三烷基硼烷笼，这些硼中心对叶立德的反应性大大降低。大约三分之二的物种在这些阶段停止聚合。然而，这些物种中的三分之一继续增长，最终导致形成窄多分散性的巨型大环聚合物。分子建模和动力学模拟有助于分析反应可能进行的途径。
