Tuning Selectivity of Anionic Cyclizations: Competition between 5-Exo and 6-Endo-Dig Closures of Hydrazides of <i>o-</i>Acetylenyl Benzoic Acids and Based-Catalyzed Fragmentation/Recyclization of the Initial 5-Exo-Dig Products
作者:Sergey F. Vasilevsky、Tat’yana F. Mikhailovskaya、Victor I. Mamatyuk、Georgy E. Salnikov、Georgy A. Bogdanchikov、Mariappan Manoharan、Igor V. Alabugin
DOI:10.1021/jo901551g
日期:2009.11.6
nucleophile is controlled by the nature of alkyne substituents under the kinetic control conditions. In the presence of KOH, the initially formed 5-exo products undergo a new rearrangement that involves a ring-opening followed by recyclization to the formal 6-exo-products and rendered irreversible by a prototropic isomerization. DFT computations provide insight into the nature of factors controlling relative
根据反应条件和三键上取代基的性质,邻位酰肼的阴离子环化乙炔基苯甲酸可选择性地沿着三种替代途径被引导,每种途径均能有效地进入不同类别的氮杂环。“内部”氮亲核试剂的5-exo和6-endo环化之间的竞争由动力学控制条件下炔烃取代基的性质控制。在KOH的存在下,最初形成的5-exo产物经历了新的重排,该新的重排涉及开环,然后环化成正式的6-exo产物,并且由于质子异构化而变得不可逆。DFT计算可洞悉控制5-exo,6-endo和6-exo环化路径的相对速率的因素的性质,从而确定直接进行6-exo封闭的可行性以及该过程中阴离子前体的相对稳定性,首次获得了几类阴离子氮环化的基准数据,并剖析了控制环阴离子中间体相对稳定性并影响反应立体选择性的立体电子效应。我们表明,在这种情况下,通过将稳定的氮阴离子转变为本质上不稳定的碳负离子,可以抵消由于将弱的π键转变为更强的σ键(炔烃环化的通常驱动力)而获得的稳定