Experimental and Computational Studies on Interrupted Nazarov Reactions: Exploration of Umpolung Reactivity at the a-Carbon of Cyclopentanones

A set of densely substituted, alpha-functionalized cyclopentanones can be generated by a two-component, domino reaction sequence entailing the Nazarov electrocyclization of divinyl ketones and nucleophilic addition of the resulting 2-oxidocyclopentenyl cations by selected trapping modalities. Bypass...

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Published inJournal of the American Chemical Society Vol. 136; no. 42; pp. 14903 - 14911
Main Authors Wu, Yen-Ku, Dunbar, Christine R., McDonald, Robert, Ferguson, Michael J., West, F. G.
Format Journal Article
LanguageEnglish
Published WASHINGTON Amer Chemical Soc 22.10.2014
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
ALLYL CATIONS
CYCLOADDITION REACTIONS
DIELS-ALDER REACTIONS
BOND-FORMING REACTIONS
SOMO CATALYSIS
OXYALLYL CATIONS
STEREOSELECTIVE-SYNTHESIS
CYCLIZATION
QUANTUM-CHEMICAL CHARACTERIZATION
ALLENYL VINYL KETONES
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Summary:A set of densely substituted, alpha-functionalized cyclopentanones can be generated by a two-component, domino reaction sequence entailing the Nazarov electrocyclization of divinyl ketones and nucleophilic addition of the resulting 2-oxidocyclopentenyl cations by selected trapping modalities. Bypassing the typical eliminative termination, Nazarov oxyallyl species can react with carbon p-nucleophiles through cycloadditions (or formal cycloadditions), in which bridged bicyclic systems are established, or nucleophilic trappings whereby one terminal carbon of the oxyallyl intermediate is subjected to carbon-carbon bond formation. A detailed investigation of reaction parameters to explicitly control the course of the "interrupted" Nazarov reactions is described. This methodology allows for facile installation of alpha-quaternary centers bearing allyl, alkynyl, and heteroaryl groups in an umpolung fashion. In addition, the trapping event of a Nazarov intermediate with furan was studied by DFT computations, in conjunction with experimental data, offering a rationale for the observed reaction pattern and diastereoselectivity.
ISSN:0002-7863
DOI:10.1021/ja507638r