Notable effect of an electron-withdrawing group at C3 on the selective formation of alkylidenecyclobutanes in the thermal denitrogenation of 4-spirocyclopropane-1-pyrazolines. Nonstatistical dynamics effects in the denitrogenation reactions
Notable effect of an electron-withdrawing group at C3 on the selective formation of alkylidenecyclobutanes in the thermal denitrogenation of 4-spirocyclopropane-1-pyrazolines. Nonstatistical dynamics effects in the denitrogenation reactions
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DOI：
10.1021/ja068513e
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发表时间：
2007-10-31
影响因子：
15
通讯作者：
Abe, Manabu
中科院分区：
文献类型：
--
作者：
Hamaguchi, Masashi;Nakaishi, Masahiro;Abe, Manabu
详细研究了3-甲氧羰基取代的4-螺环丙烷-1-吡唑啉6的热脱氮反应。亚烷基环丁烷衍生物7以立体特异性方式选择性地形成。对1-吡唑啉10a的非限制密度泛函计算表明，2个C-N键的协同断裂是脱氮反应得到2-螺环丙基1，3-二基的能量优势过程，然后是一个同旋闭环过程，计算得到的能量最小路径，得到螺戊烷衍生物.计算的能量最小途径与6和10a的脱氮实验结果基本不一致。通过考虑协同脱氮反应中的非统计动力学效应，解决了实验结果与标准计算结果之间的矛盾。虽然从3-烷氧羰基取代的1-吡唑啉的协同脱氮的过渡态的能量最小途径涉及相应的1，3-双自由基的产生，许多轨迹计算。采用Bohn-Oppenheimer分子动力学模型，在UB 3LYP/6- 31 G（d）水平上从过渡态进行协同脱氮反应，直接导致了亚烷基环丁烷的生成。
A detailed study of the thermal denitrogenation of 3-carbomethoxy-substituted 4-spirocyclopropane- 1-pyrazolines 6 was conducted. Alkylidenecyclobutane derivatives 7 were selectively formed in a stereospecific manner. Unrestricted density functional calculations for a 1-pyrazoline 10a indicated that the concerted cleavage of two C-N bonds is the energetically favored process for the denitrogenation reaction to give the 2-spirocyclopropyl 1,3-diyl, followed by a conrotatory ring-closure process, which was calculated to be the energy minimum pathway, to afford a spiropentane derivative. The calculated energy minimum pathway is largely inconsistent with the experimental results observed for the denitrogenation of 6 and 10a. The contradiction between the experimental and standard computational results was solved by considering nonstatistical dynamics effects in the concerted denitrogenation reactions. Although the energy minimum pathway from the transition states of the concerted denitrogenation of the 3-carboalkoxy-substituted 1-pyrazolines involves generation of the corresponding 1,3-diradicals, many trajectory calculations. using the Bohn -Oppenheimer molecular dynamics model from the transition state for the concerted denitrogenation led directly to the formation of alkylidenecyclobutanes at the UB3LYP/6-31G(d) level of theory.