Competitive formation of helical cycloocta- and cyclododecapyrroles.
Competitive formation of helical cycloocta- and cyclododecapyrroles.
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螺旋环八吡咯和环十二吡咯的竞争形成。
DOI：
10.1021/jo0011890
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
E. Vogel
中科院分区：
文献类型：
--
作者：
J. Wytko;M. Michels;L. Zander;J. Lex;H. Schmickler;E. Vogel
在一项旨在评估螺二咯咯 (1a) 及其双核 Ni(II) 配合物 (1b) 电子效应的研究中，我们对偕二甲基取代的环四吡咯 (2a) 和相应的 Ni(II) 配合物 (2b) 产生了兴趣。尝试通过二甲基二吡基甲烷 3 和二甲酰联吡咯 4 的酸催化 (1 + 1) 缩合制备 2a 作为 12,13,16,17-四乙基-2,3,7,8-四甲基衍生物 (5)，导致形成 (2 + 2) 和 (3 + 3) 缩合产物，即环八吡咯分别为环十二吡咯6和环十二吡咯7，而不是所需的偕二甲基环四吡咯。环十二吡咯 7 作为主要产物被分离出来，是迄今为止已知的最大的环聚吡咯之一。这两种新的大环化合物已通过变温一维和二维核磁共振实验以及单晶 X 射线衍射分析进行了结构表征。在溶液中，环八吡咯 6 和环十二吡咯 7 均表现出动态行为。在 337 K 6 处采用 D(2) 对称构象，而在 196 K 处观察到两个等效的 C(2) 构象异构体通过 D(2) 对称中间体相互转化。发现这两种简并构象异构体之间相互转化过程的能垒为 10.6 kcal mol(-)(1)。 7 的溶液动力学可以用类似的方式描述，378 K 时的时间平均构象显示 D(3)(h)() 对称性。 X 射线分析表明，对于两种大环化合物 6 和 7，其固态结构几乎与低温溶液构象异构体相同。
In connection with a study aimed at the evaluation of electronic effects in spiro-dicorrole (1a) and its binuclear Ni(II) complex (1b) we became interested in gem-dimethyl-substituted cyclotetrapyrrole (2a) and the corresponding Ni(II) complex (2b). Attempts to prepare 2a as the 12,13,16,17-tetraethyl-2,3,7, 8-tetramethyl derivative (5) by an acid-catalyzed (1 + 1) condensation of dimethyldipyrrylmethane 3 and diformylbipyrrole 4 resulted in the formation of the (2 + 2) and (3 + 3) condensation products, i.e., the cyclooctapyrrole 6 and the cyclododecapyrrole 7, respectively, rather than in that of the desired gem-dimethyl cyclotetrapyrrole. The cyclododecapyrrole 7, isolated as the major product, is among the largest cyclopolypyrroles known to date. These two new macrocycles have been structurally characterized by variable temperature 1D and 2D NMR experiments, as well as by single-crystal X-ray diffraction analysis. In solution both the cyclooctapyrrole 6 and cyclododecapyrrole 7 exhibit dynamic behavior. At 337 K 6 adopts a D(2)-symmetric conformation, whereas at 196 K two equivalent C(2) conformers that interconvert through the D(2)-symmetric intermediate are observed. The energy barrier for the interconversion process between these two degenerate conformers is found to be 10.6 kcal mol(-)(1). The solution dynamics of 7 could be described in an analogous manner, with the time-averaged conformation at 378 K displaying D(3)(h)() symmetry. X-ray analyses showed that for both macrocycles, 6 and 7, the solid state structures were nearly identical to the low-temperature solution conformers.