Antiaromaticity Gain Activates Tropone and Nonbenzenoid Aromatics as Normal-Electron-Demand Diels–Alder Dienes

We propose a carbonyl umpolung strategy for activating tropone as a normal-electron-demand Diels–Alder diene. Tropone has low reactivity for Diels–Alder reactions because of its [4n+2] π-aromaticity. Conversion of the carbonyl group into a hydrazone ion (N–NR–) reverses the polarity of the exocycli...

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Bibliographic Details
Published inOrganic letters Vol. 22; no. 18; pp. 7083 - 7087
Main Authors Karas, Lucas J, Campbell, Adam T, Alabugin, Igor V, Wu, Judy I
Format Journal Article
LanguageEnglish
Published United States American Chemical Society 18.09.2020
Subjects
aromatic compounds
cycloaddition reactions
energy
hydrazones
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Summary:We propose a carbonyl umpolung strategy for activating tropone as a normal-electron-demand Diels–Alder diene. Tropone has low reactivity for Diels–Alder reactions because of its [4n+2] π-aromaticity. Conversion of the carbonyl group into a hydrazone ion (N–NR–) reverses the polarity of the exocyclic double bond, increases the [4n] ring π-antiaromaticity, and raises the HOMO energy. Computed gas-phase activation free energies for a Diels–Alder reaction with maleimide suggest a billion-fold rate increase when the tropone CO is replaced by N–NR– (R = H or SO2CH3). Other nonbenzenoid aromatics can be activated as normal-electron-demand Diels–Alder dienes in the same way.
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ISSN:1523-7060
1523-7052
1523-7052
DOI:10.1021/acs.orglett.0c02343