How the Binding of Substrates to a Chiral Polyborate Counterion Governs Diastereoselection in an Aziridination Reaction: H-Bonds in Equipoise
How the Binding of Substrates to a Chiral Polyborate Counterion Governs Diastereoselection in an Aziridination Reaction: H-Bonds in Equipoise
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DOI：
10.1021/ja103863j
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发表时间：
2010-09-29
影响因子：
15
通讯作者：
Wulff, William D.
中科院分区：
文献类型：
--
作者：
Vetticatt, Mathew J.;Desai, Aman A.;Wulff, William D.
采用ONIOM（B3 LYP/6- 31 G *：AM 1）方法研究了MEDAM亚胺与三种典型的重氮亲核试剂在自组装手性Bronsted酸催化下的氮杂环丙烷化反应的立体化学决定步骤.重氮乙酸乙酯反应中顺式选择性和N-苯基重氮乙酰胺反应中反式选择性的起源可以根据立体化学决定过渡态中特定非共价相互作用的差异来理解。手性对映体的手性氢和氧原子之间的氢键相互作用已被确定为导致这种非对映选择性逆转的关键相互作用。当缺乏这种相互作用的3度重氮酰胺在实验和计算上都表现出明显的顺式选择性时，这一假设得到了验证。在三氟甲磺酸催化的类似反应中观察到类似的非对映选择趋势。广泛的影响，这些研究结果和它们的相关性手性布朗斯台德酸催化进行了讨论。
The stereochemistry-determining step of the self-assembled chiral Bronsted acid-catalyzed aziridination reactions of MEDAM imines and three representative diazo nucleophiles has been studied using ONIOM(B3LYP/6-31G*:AM1) calculations. The origin of cis selectivity in the reactions of ethyldiaz-oacetate and trans selectivity in reactions of N-phenyldiazoacetamide can be understood on the basis of the difference in specific noncovalent interactions in the stereochemistry-determining transition state. A H-bonding interaction between the amidic hydrogen and an oxygen atom of the chiral counterion has been identified as the key interaction responsible for this reversal in diastereoselectivity. This hypothesis was validated when a 3 degrees diazoamide lacking this interaction showed pronounced cis selectivity both experimentally and calculationally. Similar trends in diastereoselection were observed in analogous reactions catalyzed by triflic acid. The broad implications of these findings and their relevance to chiral Bronsted acid catalysis are discussed.