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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/12904

Title: 1, 3-Dipolar cycloaddition reactions of selected 1,3-dipoles with 7- isopropylidenenorbornadiene and follow-up thermolytic cleavage: A computational study
Authors: Arhin, Grace
Adams, Anita Houston
Opoku, Ernest
Tia, Richard
Adei, Evans
Keywords: Density functional theory
Norbornadiene
Isoxazolidines 1,3-Dipoles
Reaction mechanism
Issue Date: 8-Aug-2019
Publisher: Elsevier Inc.
Abstract: The mechanism, regio-, stereo-, and enantio-selectivities of the 1,3-dipolar cycloaddition reactions of 7- isopropylidenenorbornadiene (DENBD) with nitrones and azides to form pharmaceutically relevant isoxazolidine and triazole analogues have been studied computationally at the M06/6-31G(d), 6- 31G(d,p), 6-311G(d,p), 6e311þþG(d,p) and M06-2X/6-31G(d) levels of theory. In the reactions of DENBD with phenyl nitrones, the cycloaddition steps have low activation barriers, with the highest being 16 kcal/ mol; and the Diels-Alder cycloreversion steps have generally high barriers, with the lowest being 20 kcal/ mol, suggesting that the isolable products in these reactions are the bicyclic isoxazolidine cycloadducts and not the thermolytic products. This is in contrast to the reactions of DENBD with phenyl azide where the isolable products are predicted to be the thermolytic products since the Diels-Alder cycloreversion steps had relatively lower activation barriers. Electron-donating substituents on the dipolarophile substrate favour attack of the nitrone on the least hindered side of the DENBD substrate while electronwithdrawing substituents on the dipolarophile substrate favour attack on the more hindered side of the DENBD, indicating that site-selectivity is affected by nature of substituents. Global reactivity indices calculations are in good agreement with the activation barriers obtained. Analysis of the electrophilic (Pþ K Þ and nucleophilic (P K Þ Parr functions at the reactive centres reveal that the cycloaddition occurs between atoms with the largest Mulliken and NBO atomic spin densities which agrees well with the energetic trends and the experimental product outcomes.
Description: An article published by Elsevier Inc. and also available at https://doi.org/10.1016/j.jmgm.2019.08.004
URI: http://hdl.handle.net/123456789/12904
Appears in Collections:College of Science

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