On the importance of leaving group ability in reactions of ammonium, oxonium, phosphonium, and sulfonium ylides
On the importance of leaving group ability in reactions of ammonium, oxonium, phosphonium, and sulfonium ylides
复制标题
DOI：
10.1002/anie.200501526
复制
发表时间：
2005-01-01
影响因子：
16.6
通讯作者：
Robiette, R
中科院分区：
文献类型：
--
作者：
Aggarwal, VK;Harvey, JN;Robiette, R
在有机化学中，叶立德是一种功能强大、用途广泛的试剂，它们经历了三种重要的反应：烯化反应、环化成三元环和重排反应。叶立德碳中心的亲核性是其反应性的一个重要方面，这一点受到铀基稳定相邻负电荷的程度的影响。结果表明，稳定度按O<；N！然而，这一特征本身并不能解释所有观察到的反应性。我们提供了比较计算数据，这些数据表明，差异主要是由于各自的铀组的不同的离开组能力。计算[3]是使用精确的B3LYP密度泛函进行的，该密度泛函被认为能准确地描述这里研究的那种趋势。[4，5]我们还在所有计算中包括了一个连续介质溶剂模型，因为对于这些非常极性的物种中的一些，气相势能面在定性上是不准确的。[5]在与有机硼烷的反应中，硫叶立德在低温下产生同系化产物[6]，而更亲核的叶立德只在四氢呋喃的回流下反应，[7]而膦叶立德需要1308℃以上的温度。[8]BMe3与叶立德1反应的能量分布[3]涉及无障碍加成以形成ATE络合物2，随后是决定速度的1，2迁移(图1)。第一步对氨基和氧基叶立德的放热最大，对氧基叶立德的迁移阻挡最小，对膦衍生物的迁移阻挡最大。俄叶立德的亲核性显然与这一过程无关，
Ammonium, phosphonium, and sulfonium ylides are powerful and versatile reagents in organic chemistry, which undergo three important types of reaction: olefination, cyclization to a three-membered ring, and rearrangement.[1] The reactivity and selectivity of the ylides in these reactions depend on the nature of the central heteroatom. The nucleophilicity of the carbon centre of the ylides is one important aspect of their reactivity, which is affected by the degree to which the onium group stabilizes the adjacent negative charge. It has been shown that stabilization increases in the order O< N! P< S.[2] However, this feature alone does not explain all the observed reactivity. We present comparative computational data which suggest that the differences are mainly due to the differing leaving group ability of the respective onium groups. The calculations [3] are carried out using the accurate B3LYP density functional, which is known to describe trends of the kind studied here accurately.[4, 5] We also include a continuum solvent model in all calculations as the gas-phase potential energy surfaces are qualitatively inaccurate for some of these very polar species.[5]In the reaction with organoboranes, sulfonium ylides give homologation products at low temperature [6] while the more nucleophilic ammonium ylides react only at reflux of THF,[7] and phosphonium ylides require temperatures above 1308C.[8] The energy profile [3] for the reaction of BMe3 with ylides 1 involves barrierless addition to form ate complex 2, followed by rate-determining 1, 2-migration (Figure 1). The first step is most exothermic for the ammonium and oxonium ylides while the barrier for migration is smallest with the oxonium ylide and largest with the phosphonium derivative. Nucleophilicity of the onium ylides is clearly irrelevant for this process, with