Diels–Alder Reactivities of Benzene, Pyridine, and Di-, Tri-, and Tetrazines: The Roles of Geometrical Distortions and Orbital Interactions

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• 作者：Yun-Fang Yang ; Yong Liang ; Fang Liu ; K. N. Houk
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：February 10, 2016
• 年：2016
• 卷：138
• 期：5
• 页码：1660-1667
• 全文大小：690K
• ISSN：1520-5126

文摘

The cycloadditions of benzene and ten different azabenzenes (pyridine, three diazines, three triazines, and three tetrazines) with the ethylene dienophile have been explored with density functional theory (M06-2X) and analyzed with the distortion/interaction model. Activation barriers correlate closely with both distortion energies and interaction energies over an activation energy range of 45 kcal/mol. The replacement of CH with N increases Diels–Alder reactivity due not only to the more favorable orbital interaction, but also to a decrease in distortion energy. The rates of reactions are greatly influenced by the nature of the bonds being formed: two C—C bonds > one C—C bond, and one C—N bond > two C—N bonds. The activation energy of Diels–Alder reactions correlates very well with reaction energies and with the NICS(0) values of the aromatic dienes. The distortion energy of the Diels–Alder reaction transition states mostly arises from the diene out-of-plane distortion energy.