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Facile Preparation of 2Z,4E-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate
Published on: June 21, 2017
Generation and trapping of electron-deficient 1,2-cyclohexadienes. Unexpected hetero-Diels-Alder reactivity
Baolei Wang1, Marius-Georgian Constantin2, Simarpreet Singh3
1Department of Chemistry, University of Alberta, E3-43 Gunning-Lemieux Chemistry Centre, Edmonton, AB, Canada T6G 2G2. frederick.west@ualberta.ca and State-Key Laboratory of Elemento-Organic Chemistry, Collaborative Innovation Center of Chemical Science and Engineering, College of Chemistry, Nankai University, Tianjin 300071, P. R. China.
Abstract:
Keto-substituted 1,2-cyclohexadienes were generated by base-mediated (KOt-Bu) elimination, and found to dimerize via an unprecedented formal hetero-Diels-Alder process, followed by hydration. These highly reactive cyclic allene intermediates were also trapped in Diels-Alder reactions by furan, 2,5-dimethylfuran, or diphenylisobenzofuran to afford cycloadducts with high regio- and diastereoselectivity, and could also be intercepted in a hetero-Diels-Alder process with enamine dienophiles. Endo/exo stereochemistry was unambiguously determined via X-ray crystallography in the case of nitrile-substituted 1,2-cyclohexadiene. DFT calculations indicate that the novel hetero-Diels-Alder processes observed with these allenes occur via a concerted asynchronous cycloaddition mechanism.
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