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Issue 3, 2019
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Unveiling the high reactivity of cyclohexynes in [3 + 2] cycloaddition reactions through the molecular electron density theory

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Abstract

[3 + 2] cycloaddition (32CA) reactions of cyclohexyne, a cyclic strained acetylene, with methyl azide and methoxycarbonyl diazomethane have been studied within the Molecular Electron Density Theory (MEDT) at the MPWB1K/6-311G(d) computational level. These 32CA reactions, which take place through a one-step mechanism involving highly asynchronous transition state structures, proceed with relatively low activation enthalpies of 6.0 and 4.3 kcal mol−1, respectively, both reactions being strongly exothermic. The reactions are initiated by the creation of a pseudoradical center at one of the two acetylenic carbons of cyclohexyne with a very low energy cost, 1.0 kcal mol−1, which promotes the easy formation of the first C–N(C) single bond in the adjacent acetylenic carbon. This scenario is completely different from that of the 32CA reaction involving non-strained but-2-yne; thus, strain in cyclohexyne triggers a high reactivity as a consequence of its unusual electronic structure at the ground state. Finally, the experimental regioselectivity of the 32CA reactions involving 3-alkoxy-cyclohexyne derivatives is correctly explained within MEDT.

Graphical abstract: Unveiling the high reactivity of cyclohexynes in [3 + 2] cycloaddition reactions through the molecular electron density theory

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Publication details

The article was received on 16 Oct 2018, accepted on 04 Dec 2018 and first published on 04 Dec 2018


Article type: Paper
DOI: 10.1039/C8OB02568A
Citation: Org. Biomol. Chem., 2019,17, 498-508

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    Unveiling the high reactivity of cyclohexynes in [3 + 2] cycloaddition reactions through the molecular electron density theory

    L. R. Domingo, M. Ríos-Gutiérrez and P. Pérez, Org. Biomol. Chem., 2019, 17, 498
    DOI: 10.1039/C8OB02568A

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