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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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