Antiaromaticity Gain Activates Tropone and Nonbenzenoid Aromatics as Normal-Electron-Demand Diels–Alder Dienes
Lucas J. Karas, Adam T. Campbell, Igor V. Alabugin, Judy I. Wu
Abstract
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.
Topics & Concepts
TroponeChemistryAntiaromaticityAromaticityUmpolungDiels–Alder reactionPnictogenPhotochemistryMedicinal chemistryReactivity (psychology)Organic chemistryCatalysisMoleculeNucleophileMedicineAlternative medicinePathologySuperconductivityPhysicsQuantum mechanicsSynthesis and Properties of Aromatic CompoundsAxial and Atropisomeric Chirality SynthesisAsymmetric Synthesis and Catalysis