开发有效的新型超级碱的挑战包括它们易于合成、化学稳定性和高碱度,同时最小化亲核性对于减少不需要的副反应很重要。在这里,我们介绍了一个新的有机超级碱家族,即紧凑型胺-冠醚轮烷,它们在所有这些方面都表现出令人满意的特性。无金属活性模板合成提供了一系列在封端基团之间只有三个原子的轮烷,锁定了轴胺基上的小冠醚(21C7 和 24C8 衍生物)的位置。互锁的亲原性组分的强制接近导致 p K a H +值在乙腈中高达 32.2,这高达 13 p K aH +单位大于非互锁组分的p K a H +值,并将游离碱轮烷带入磷腈超碱的碱度范围。轮烷超级碱通常化学稳定,并且在超级碱的模型反应中,从伯烷基溴化物中消除 HBr,完全选择性地去质子化而不是烷基化。它们适中的尺寸、易于合成、高碱度、低亲核性,以及在最好的情况下,快速的底物去质子动力学和出色的水解稳定性使得紧凑的胺-冠醚轮烷超级碱成为合成、超分子和材料化学中潜在应用的诱人候选者。
Template effects. 7. Large unsubstituted crown ethers from polyethylene glycols: Formation, analysis, and purification
作者:Chiara Antonini Vitali、Bernardo Masci
DOI:10.1016/s0040-4020(01)80080-6
日期:1989.1
tri- to deca-ethylene glycol yields not only the corresponding crownethers but also higher cyclooligomers that can be analyzed up to about [60] crown-20 by glc: in particular [36] crown-12 and [48] crown-16 were obtained from tetraethylene glycol and purified by column chromatography on cellulose; iii) the reaction, as applied to commercial mixtures of polyethyleneglycols (from PEG 200 to PEG 1000)
POTASSIUM FLUORIDE ON ALUMINA AS BASE FOR CROWN ETHER SYNTHESIS
作者:Junko Yamawaki、Takashi Ando
DOI:10.1246/cl.1980.533
日期:1980.5.5
Alumina coated with potassium fluoride was found to be an effective and practical reagent for the synthesis of some simple crown ethers.
发现涂有氟化钾的氧化铝是合成一些简单冠醚的有效且实用的试剂。
Host–guest interactions template: the synthesis of a [3]catenane
作者:Amy L. Hubbard、Gregory J. E. Davidson、Roopa H. Patel、James A. Wisner、Stephen J. Loeb
DOI:10.1039/b312449e
日期:——
Formation of a [3]catenane containing dibenzo-24-crown ether wheels and a large dipyridiniumethane ring is templated by formation of a host-guest adduct between the [3]catenane and the external crown ether.
Iron(ii) complexes utilising terpyridine containing [2]rotaxanes as ligands
作者:Gregory J. E. Davidson、Stephen J. Loeb
DOI:10.1039/b308553h
日期:——
A terpyridine chelating group is incorporated into a cationic (dipyridinium)ethane axle and self-assembly synthesis used to create three [2]rotaxanes utilising 24-membered crown ether wheels: 24-crown-8, dibenzo-24-crown-8 and dinaphtho-24-crown-8 ether. The resulting [2]rotaxanes are characterised by 1H NMR spectroscopy, X-ray crystallography and mass spectrometry. The ability of these rotaxanes to
24-crown-8 in the reaction of tetraethylene glycol/TsCl/Na(K)OH in dioxane, 12-crown-4 was obtained in a moderate yield from the reaction of tetraethylene glycol/benzenesulfonyl chloride/t-BuOLi in t-BuOH. Furthermore, the analogous treatment of PEG 200 afforded a mixture of 15-, 18-, 21-, and 24-crown ethers. The reaction conditions were investigated, and the scope of the reaction was discussed.