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<p>Diels–Alder (DA) cycloadditions are potent atom-economical transformations for the formation of six-membered cycloadducts with excellent regio- and stereoselectivity. The DA 4 + 2 cycloaddition between furan-2-ylmethanol and <i>N</i>-phenylmaleimides with para-substituents (<i>X</i> = H, F, Cl, Br) is studied using MEDT and density functional theory calculations at the M06‑2X(D3)/6‑311G(<i>d</i>,<i>p</i>) level. The polarity of the studied cycloaddition reaction was determined using conceptual DFT (CDFT) indices, natural population analysis (NPA), and global electron density-transfer (GEDT) values to quantify the electronic properties of the reagents and track the expected flow of electron density. In all substitution patterns, <i>exo</i> path is projected to be more favorable than <i>endo</i> path. The transition states’ polarity is corroborated by high GEDT values (≈ 0.26–0.28 e), showing electron density transfer from the furan-derived diene to the maleimide framework. Electron localization function (ELF) topological analysis for reactants and transition states was combined with bonding evolution theory (BET) along intrinsic reaction coordinates (IRC) to better understand chemical bond formation and how substituents affect it. These analyses suggest a two-stage, one-step (asynchronous) cycloaddition in which the new C–C bond is formed earlier at the transition state than the second bond involving the heteroatom-containing fragment, indicating a polar, nonsynchronous bonding reorganization rather than a perfectly coordinated event. Additional QTAIM and NCI descriptions show developing interactions at the forming bond critical points and weak stabilizing noncovalent contacts that favor <i>exo</i> transition structures. Electron-withdrawing substituents enhance electrophilicity of dienophile and subtly modulate energetics and electron density redistribution along the <i>exo</i> path, explaining the impact of phenyl-ring halogen substitution.</p>

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Mechanistic insights into furan-based Diels–Alder cycloadditions: an ELF, BET, NCI, AIM, and MEDT study

  • 期刊论文

  • 发表日期：

    2026年5月16日

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  • Haydar Mohammad-Salim

摘要

Diels–Alder (DA) cycloadditions are potent atom-economical transformations for the formation of six-membered cycloadducts with excellent regio- and stereoselectivity. The DA 4 + 2 cycloaddition between furan-2-ylmethanol and N-phenylmaleimides with para-substituents (X = H, F, Cl, Br) is studied using MEDT and density functional theory calculations at the M06‑2X(D3)/6‑311G(d,p) level. The polarity of the studied cycloaddition reaction was determined using conceptual DFT (CDFT) indices, natural population analysis (NPA), and global electron density-transfer (GEDT) values to quantify the electronic properties of the reagents and track the expected flow of electron density. In all substitution patterns, exo path is projected to be more favorable than endo path. The transition states’ polarity is corroborated by high GEDT values (≈ 0.26–0.28 e), showing electron density transfer from the furan-derived diene to the maleimide framework. Electron localization function (ELF) topological analysis for reactants and transition states was combined with bonding evolution theory (BET) along intrinsic reaction coordinates (IRC) to better understand chemical bond formation and how substituents affect it. These analyses suggest a two-stage, one-step (asynchronous) cycloaddition in which the new C–C bond is formed earlier at the transition state than the second bond involving the heteroatom-containing fragment, indicating a polar, nonsynchronous bonding reorganization rather than a perfectly coordinated event. Additional QTAIM and NCI descriptions show developing interactions at the forming bond critical points and weak stabilizing noncovalent contacts that favor exo transition structures. Electron-withdrawing substituents enhance electrophilicity of dienophile and subtly modulate energetics and electron density redistribution along the exo path, explaining the impact of phenyl-ring halogen substitution.