The reaction mechanism of cycloadditions of tetrachloro-o-benzoquinone with 6,6-dimethylfulvene were systematically investigated with density functional theory calculations. It was found that conditional primary interactions stabilize the ambimodal transition states in the endo pathways. Ambimodal transition states lead to [6 + 4]/[4 + 2] adducts or [4 + 2]/[2 + 4] adducts, which interconvert through 3,3-sigmatropic shift reactions. The substituent effects on periselectivity were also investigated.
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http://dx.doi.org/10.1002/jcc.27264 | DOI Listing |
Molecules
November 2024
Henan-Macquarie University Joint Centre for Biomedical Innovation, Henan Key Laboratory of Brain Targeted Bio-Nanomedicine, School of Life Sciences, Henan University, Kaifeng 475004, China.
Post-transition state bifurcation (PTSB) is a fundamental process in which a single transition state leads to multiple products. This phenomenon is important in both biological and chemical contexts and offers valuable insights into reaction mechanisms and their applications. The theozyme model, which focuses on key residues within enzymes, offers a computationally efficient method for studying these processes while preserving the enzyme's catalytic properties.
View Article and Find Full Text PDFJ Chem Theory Comput
December 2024
Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, United States.
One ambimodal transition state can lead to the formation of multiple products. However, it remains fundamentally unknown how the energy and entropy along the post-TS pathways mediate ambimodal selectivity. Here, we investigated the energy and entropy profiles along the post-TS pathways in four [4 + 2]/[6 + 4] cycloadditions.
View Article and Find Full Text PDFJ Org Chem
December 2024
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
The mechanism of the dirhodium-catalyzed combined C-H functionalization/Cope rearrangement (CH/Cope) reaction discovered by the Davies group has been investigated with density functional theory (DFT) calculations and quasi-classical molecular dynamics (MD) simulations. Computations from the Davies group previously showed that there is a post-transition state bifurcation leading to a direct CH reaction and also to the CH/Cope product. While this work was in preparation, the Tantillo group and the Ess group independently reported quantum mechanical and molecular dynamics studies on the dirhodium-tetracarboxylate-catalyzed diazoester CH/Cope and CH insertion reactions with 1,3-cyclohexadiene and 1,4-cyclohexadiene, respectively.
View Article and Find Full Text PDFOrg Lett
September 2024
Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia.
The latent singlet diradical character of the parent -quinonedimethide (-QDM), as revealed by valence bond calculations, is demonstrated experimentally by trapping with the kinetically stable free radical TEMPO at room temperature. In the absence of TEMPO, the main pathway for decomposition at ambient temperature is not (as previously proposed in the literature) a radical reaction but instead a concerted Diels-Alder dimerization, which through ωB97X-D/aug-cc-pVTZ/SMD//M06-2X-D3/6-31+G(d,p)/SMD calculations is shown to proceed through an ambimodal bispericyclic transition state. The predominantly non-radical reactivity of -QDM at room temperature differs from that of its isomeric -quinonedimethide (-QDM) congener, which self-reacts through radical pathways.
View Article and Find Full Text PDFJ Comput Chem
December 2024
Department of Chemistry, Saitama University, Saitama, Japan.
CH (tetradecapentaene) is a simple model system exhibiting post transition-state behavior, wherein both the (6 + 4) and (4 + 2) cycloaddition products are formed from one ambimocal transition state structure. We studied the bifurcation dynamics starting from the two ambimodal transition state structures, the chair-form and boat-form, using the quasi-classical trajectory, classical molecular dynamics, and ring-polymer molecular dynamics methods on the parameter-optimized semiempirical GFN2-xTB potential energy surface. It was found that the calculated branching fractions differ between the chair-form and boat-form due to the different nature in the IRC pathways.
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