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<p>The regio- and stereoselectivity, molecular mechanism, and catalytic effect of the Lewis acid (LA) AlCl<sub>2</sub>Et on the Diels-Alder (DA) reaction between methyl 3-hydroxy-2-methylenepentanoate (hydroxy-ester dienophile, HED) <b>1</b> and isoprene (IP) <b>2</b> were investigated using density functional theory within the framework of Molecular Electron Density Theory (MEDT) at the ωB97X-D/def2-TZVP level. Coordination of the AlCl<sub>2</sub>Et significantly activates the dienophile HED <b>1</b> and lowers the activation energies of the transition state structure (TS), thereby accelerating the DA reaction. The calculated free energy profiles indicate that the reaction preferentially proceeds through the <i>exo</i> pathway, leading to the <i>exo</i> DA adduct as the major product. The high global electron density transfer (GEDT) values obtained from natural bond orbital (NBO) analysis indicate a polar character, while bonding evolution theory (BET) analysis shows that the reaction proceeds through a highly asynchronous one-step bond formation process, with the two C–C bonds forming to different extents at the TS. In addition, a predictive investigation of an alternative HACD <b>4</b> shows that this substrate exhibits lower activation barriers than HED <b>1</b> in the presence of the AlCl<sub>2</sub>Et catalyst, suggesting enhanced reactivity for the DA reaction.</p>

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Theoretical insights into the mechanism of Lewis acid-catalysed Diels-Alder reaction between hydroxy-ester dienophile and isoprene: origin of regio- and stereoselectivity

  • 期刊论文

  • 发表日期：

    2026年5月6日

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  • Ravi Bariya,
  • Ankit Patel,
  • Sangita Sharma

摘要

The regio- and stereoselectivity, molecular mechanism, and catalytic effect of the Lewis acid (LA) AlCl2Et on the Diels-Alder (DA) reaction between methyl 3-hydroxy-2-methylenepentanoate (hydroxy-ester dienophile, HED) 1 and isoprene (IP) 2 were investigated using density functional theory within the framework of Molecular Electron Density Theory (MEDT) at the ωB97X-D/def2-TZVP level. Coordination of the AlCl2Et significantly activates the dienophile HED 1 and lowers the activation energies of the transition state structure (TS), thereby accelerating the DA reaction. The calculated free energy profiles indicate that the reaction preferentially proceeds through the exo pathway, leading to the exo DA adduct as the major product. The high global electron density transfer (GEDT) values obtained from natural bond orbital (NBO) analysis indicate a polar character, while bonding evolution theory (BET) analysis shows that the reaction proceeds through a highly asynchronous one-step bond formation process, with the two C–C bonds forming to different extents at the TS. In addition, a predictive investigation of an alternative HACD 4 shows that this substrate exhibits lower activation barriers than HED 1 in the presence of the AlCl2Et catalyst, suggesting enhanced reactivity for the DA reaction.