Haberhauer Gebhard, Gleiter Rolf, Woitschetzki Sascha
Institut für Organische Chemie, Universität Duisburg-Essen , Universitätsstrasse 7, D-45117 Essen, Germany.
Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany.
J Org Chem. 2015 Dec 18;80(24):12321-32. doi: 10.1021/acs.joc.5b02230. Epub 2015 Nov 24.
By means of high level quantum chemical calculations (B2PLYPD and CCSD(T)), the mechanisms of the reaction of nitrile oxides with alkenes and alkynes were investigated. We were able to show that in the case of alkenes, regardless of the chosen substituents, the concerted mechanism is always energetically favored as compared to a two-step process, which runs through an anti-diradical species. In the case of alkynes, the concerted mechanism is favored only for the reaction of alkyl-substituted acetylenes. For aryl-substituted acetylenes, the activation barrier toward the anti-diradical is equal to or lower than the activation barrier of the concerted reaction. This reversal of the reaction paths is not only limited to nitrile oxides as dipolarophiles. Conditions favoring the anti-diradical path are the presence of a triple bond in both the 1,3-dipole and the dipolarophile and additionally an aryl substituent attached to the alkyne. The featured energy relationships between the reaction paths are able to explain the experimentally observed byproducts of the reaction of nitrile oxides with arylacetylenes. The discovered differences for the preferred reaction path of 1,3-dipolar cycloadditions to acetylenes should be of considerable interest to a broader field of chemists.
通过高水平量子化学计算（B2PLYPD和CCSD(T)），研究了腈氧化物与烯烃和炔烃反应的机理。我们能够表明，对于烯烃，无论选择何种取代基，与通过反双自由基物种的两步过程相比，协同机理在能量上总是更有利的。对于炔烃，协同机理仅在烷基取代乙炔的反应中占优势。对于芳基取代的乙炔，生成反双自由基的活化能垒等于或低于协同反应的活化能垒。这种反应路径的反转不仅限于作为亲偶极体的腈氧化物。有利于反双自由基路径的条件是1,3 -偶极体和亲偶极体中都存在三键，并且炔烃上还连接有芳基取代基。反应路径之间的特定能量关系能够解释腈氧化物与芳基乙炔反应实验观察到的副产物。1,3 -偶极环加成反应到乙炔的首选反应路径中发现的差异应该会引起更广泛化学领域的相当大兴趣。
