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Ambident Reactivities of Pyridone Anions

机译:吡啶酮阴离子的环境反应性

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The kinetics of the reactions of the ambident 2- and 4-pyridone anions with benzhydrylium ions (diarylcarbenium ions) and structurally related Michael acceptors have been studied in DMSO, CH3CN, and water. No significant changes of the rate constants were found when the counterion was varied (Li+, K+, NBu4+) or the solvent was changed from DMSO to CH3CN, whereas a large decrease of nucleophilicity was observed in aqueous solution. The second-order rate constants (log k2) correlated linearly with the electrophilicity parameters E of the electrophiles according to the correlation log k2 = s(N + E) (Angew. Chem., Int. Ed. Engl. 1994, 33, 938−957), allowing us to determine the nucleophilicity parameters N and s for the pyridone anions. The reactions of the 2- and 4-pyridone anions with stabilized amino-substituted benzhydrylium ions and Michael acceptors are reversible and yield the thermodynamically more stable N-substituted pyridones exclusively. In contrast, highly reactive benzhydrylium ions (4,4′-dimethylbenzhydrylium ion), which react with diffusion control, give mixtures arising from N- and O-attack with the 2-pyridone anion and only O-substituted products with the 4-pyridone anion. For some reactions, rate and equilibrium constants were determined in DMSO, which showed that the 2-pyridone anion is a 2−4 times stronger nucleophile, but a 100 times stronger Lewis base than the 4-pyridone anion. Quantum chemical calculations at MP2/6-311+G(2d,p) level of theory showed that N-attack is thermodynamically favored over O-attack, but the attack at oxygen is intrinsically favored. Marcus theory was employed to develop a consistent scheme which rationalizes the manifold of regioselectivities previously reported for the reactions of these anions with electrophiles. In particular, Kornblum’s rationalization of the silver ion effect, one of the main pillars of the hard and soft acid/base concept of ambident reactivity, has been revised. Ag+ does not reverse the regioselectivity of the attack at the 2-pyridone anion by increasing the positive charge of the electrophile but by blocking the nitrogen atom of the 2-pyridone anion.
机译:在DMSO,CH 3 CN和水中,研究了2-和4-吡啶环型阴离子与苯甲酸铵离子(二芳基碳鎓离子)和结构相关的迈克尔受体的反应动力学。改变抗衡离子(Li + ,K + ,NBu 4 + )或将溶剂从DMSO改为CH 3 CN,而在水溶液中观察到亲核性大大降低。二阶速率常数(log k 2 )根据相关性log k 2 = s(N + E)与亲电体的亲电参数E线性相关( Angew。Chem。,Int。Ed。Engl。1994,33,938-957),使我们能够确定吡啶酮阴离子的亲核参数N和s。 2-和4-吡啶酮阴离子与稳定的氨基取代的苯甲基铵离子和迈克尔受体的反应是可逆的,并且仅产生热力学上更稳定的N-取代的吡啶酮。相比之下,与扩散控制反应的高反应性苯甲酸铵离子(4,4'-二甲基苯甲酸铵离子)会产生由N-和O-攻击与2-吡啶酮阴离子产生的混合物,只有O-取代的产物与4-吡啶酮阴离子。对于某些反应,在DMSO中确定了速率常数和平衡常数,这表明2-吡啶酮阴离子比亲核试剂强2-4倍,而路易斯碱比4-吡啶酮强100倍。在MP2 / 6-311 + G(2d,p)的理论水平上进行的量子化学计算显示,在热力学上,N攻击优于O攻击,但对氧的攻击本质上是受攻击的。使用Marcus理论来开发一个一致的方案,该方案合理化了先前报道的这些阴离子与亲电试剂反应的区域选择性。特别是,柯恩布拉姆(Kornblum)对银离子效应的合理化进行了修正,这是硬和软酸/碱环境反应性概念的主要支柱之一。 Ag + 不会通过增加亲电试剂的正电荷,而是通过封堵2-吡啶酮阴离子的氮原子来逆转2-吡啶酮阴离子上的进攻的区域选择性。

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  • 来源
    《Journal of the American Chemical Society》 |2010年第43期|p.15380-15389|共10页
  • 作者单位

    Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 München, Germany;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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  • 入库时间 2022-08-18 00:50:25

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