Geminal repulsion disrupts Diels–Alder reactions of geminally substituted cyclopentadienes and 4H-pyrazoles
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nihms-1711407.pdf
Description
Accepted version
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1.14 MB
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Author(s)
Levandowski, Brian J.
Abularrage, Nile S.
Raines, Ronald T.
Date Issued
July 2021
Journal
Tetrahedron
Publisher
Elsevier BV
Citation
Levandowski, Brian J, Abularrage, Nile S and Raines, Ronald T. 2021. "Geminal Repulsion Disrupts Diels–Alder Reactions of Geminally Substituted Cyclopentadienes and 4H-Pyrazoles." Tetrahedron, 91.
Version
Author's final manuscript
Abstract
We have experimentally and computationally explored the sluggish Diels-Alder reactivities of the geminally substituted 5,5-dimethylcyclopentadiene and 5,5-dimethyl-2,3-diazacyclopentadiene (4,4-dimethyl-4H-pyrazole) scaffolds. We found that geminal dimethylation of 1,2,3,4-tetramethylcyclopentadiene to 1,2,3,4,5,5-hexamethylcyclopentadiene decreases the Diels-Alder reactivity towards maleimide by 954-fold. Quantum mechanical calculations revealed that the decreased Diels-Alder reactivities of gem-dimethyl substituted cyclopentadienes and 2,3-diazacyclopentadienes are not a consequence of unfavorable steric interactions between the diene and dienophile as reported previously, but a consequence of the increased repulsion within the gem-dimethyl group in the transition state. The findings have implications for the use of cyclopentadienes in "click" chemistry.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Terms of Use
Creative Commons Attribution-NonCommercial-NoDerivs License
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DOI of Published Version
https://doi.org/10.1016/j.tet.2021.132160
