Self-association without regard to prototropy. A heterocycle that forms extremely stable quadruply hydrogen-bonded dimers
Self-association without regard to prototropy. A heterocycle that forms extremely stable quadruply hydrogen-bonded dimers
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DOI：
10.1021/ja981884d
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发表时间：
1998-09-23
影响因子：
15
通讯作者：
Zimmerman, SC
中科院分区：
文献类型：
--
作者：
Corbin, PS;Zimmerman, SC
有一个持续的挑战，开发一套不同的分子亚基的超分子组装。1沿着这些路线，我们有一个长期的兴趣，在杂环能够形成强大的氢键在溶液中的配合物。[2，3]然而，以这种方式使用杂环可能会因质子转移而变得复杂。4虽然不需要的原异构体通常通过络合作用转化为所需的形式，但观察到的缔合常数（Kaspersky）会降低，并且信息含量可能会受到损害。例如，复合物1、2，含有AAA、DDD（A，D）氢键受体和供体）基序，是已知的最强的中性三氢键复合物。2，5然而，其稳定性降低，因为除了所需的1，4-二氢形式（2）之外，大部分二氢吡啶单体以氯仿-d（CDCl 3）中的非互补3，4-二氢形式（3）存在。有趣的是，质子转移并不影响所有杂环自缔合的能力。例如，2-吡啶酮可以以其内酰胺（4）或内酰亚胺（5）形式二聚化，6并形成异二聚体4、5。[7] R基团的空间分布在两种同源二聚体中相似，但在4 - 5中观察到不同的排列。
There is a continuing challenge to develop a diverse set of molecular subunits for supramolecular assembly. 1 Along these lines, we have a long-standing interest in heterocycles capable of forming robust hydrogen-bonded complexes in solution. 2, 3 The use of heterocycles in this manner can, however, be complicated by prototropy. 4 Although undesirable protomers are often converted to the desired form by complexation, the observed association constants (Kassoc) are lowered, and the information content can be compromised. For example, complex 1 ‚2, containing an AAA ‚DDD (A, D) hydrogen-bond acceptor and donor) motif, is the strongest, neutral triply hydrogen-bonded complex known. 2, 5 However, its stability is lowered because in addition to the desired 1, 4-dihydro form (2), a significant portion of the dihydropyridine monomer exists as the noncomplementary 3, 4-dihydro form (3) in chloroform-d (CDCl3). 2aInterestingly, prototropy does not compromise the ability of all heterocycles to self-associate. For example, 2-pyridone can dimerize in its lactam (4) or lactim (5) form, 6 and form heterodimer 4 ‚5. 7 The spatial disposition of the R groups is similar in both homodimers, but a different arrangement is seen in 4 ‚5.