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Issue 8, 2014
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Theoretical investigations toward the tandem reactions of N-aziridinyl imine compounds forming triquinanes via trimethylenemethane diyls: mechanisms and stereoselectivity

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Abstract

In this paper, we have investigated the tandem reaction mechanism for the N-aziridinyl imine compounds forming triquinanes via trimethylenemethane (TMM) diyls in detail. Based on the calculated results, the reaction is initiated by the cleavage of the N-aziridinyl in the substrate, followed by an intramolecular 1,3-dipolar (3 + 2) cycloaddition preferentially leading to a linearly-fused tetrahydrocyclopentapyrazole intermediate. Next, the intermediate loses N2 to form the singlet TMM diyl M3S, which can then undergo another concerted (3 + 2) cycloaddition to generate the linearly-fused cistrans or cissyn triquinane products. In addition, M3S can also undergo intersystem crossing to the triplet TMM diyl M3T, and the six possible reaction pathways associated with M3T have also been identified. The calculated results reveal that the cistrans fused pathway associated with M3S is energetically preferred with the highest free energy barrier of 25.0 kcal mol−1. In comparison, the cyclization of M3T requires much higher activation free energies (ΔG = 34.4–57.8 kcal mol−1). At the experimental temperature 110 °C, only the linearly-fused cistrans and cissyn pathways associated with M3TG = 34.4 and 35.5 kcal mol−1 respectively) are possible. The calculated results also indicate that for both M3S and M3T, the linearly-fused cistrans triquinane should be the main product, which is consistent with the experimental observation. At last, conformational and NBO analyses on key transition states identified the cistrans stereocontrol factors. Further calculations indicate that the methyl substituent on the allene group of the reactant substrate improves the stereoselectivity of the reaction but does not affect the rate-determining step.

Graphical abstract: Theoretical investigations toward the tandem reactions of N-aziridinyl imine compounds forming triquinanes via trimethylenemethane diyls: mechanisms and stereoselectivity

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Publication details

The article was received on 24 Oct 2013, accepted on 25 Nov 2013 and first published on 25 Nov 2013


Article type: Paper
DOI: 10.1039/C3OB42115E
Citation: Org. Biomol. Chem., 2014,12, 1220-1231
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    Theoretical investigations toward the tandem reactions of N-aziridinyl imine compounds forming triquinanes via trimethylenemethane diyls: mechanisms and stereoselectivity

    Y. Qiao and K. Han, Org. Biomol. Chem., 2014, 12, 1220
    DOI: 10.1039/C3OB42115E

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