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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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Adobe PDF
Checksum (MD5)
e170a8d2dbf9e8c52e3bdc671c53ce10
Author(s)
Levandowski, Brian J
Abularrage, Nile S
Raines, Ronald T
Date Issued
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.
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Creative Commons Attribution-NonCommercial-NoDerivs License
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DOI of Published Version
10.1016/J.TET.2021.132160
