Bayer, Patrick and Schachtner, Josef and Majek, Michal and Jacobi von Wangelin, Axel (2019) Visible light-mediated photo-oxygenation of arylcyclohexenes. ORGANIC CHEMISTRY FRONTIERS, 6 (16). pp. 2877-2883. ISSN 2052-4129,
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Substituted styrenes constitute important molecular building blocks for various synthetic manipulations, including selective core and peripheral oxidations. The photo-oxidation of such substrates by a singlet oxygen ene reaction (Schenck ene reaction) is especially attractive as it relies upon the combination of three abundant and cheap components: air, visible light, and an organic dye. The resultant allyl hydroperoxides enable various functionalizations to alcohols, carbonyls, epoxides, triols etc. The synthetic potential and mechanistic minutiae of photo-oxidations of styrene derivatives are not fully understood and were hitherto explored only for a very limited set of substrates. The operation of multiple oxidation events, low selectivities and yields have limited further applications of this method. Now this study reports a concise investigation of such photo-oxidations of diverse cycloalkenylbenzenes under continuous flow conditions. The combination of synthetic, kinetic, spectroscopic, and thereotical data enabled us to provide a detailed mechanistic rationalization of the observed reactivities and chemoselectivities. We propose a rarely discussed zwitterionic key intermediate of the observed allylic and [4 + 2]-dioxygenations based on a detailed Hammett study and DFT calculations. The reaction conditions of such photo-oxidations have been optimized to allow short reaction times (<10 min), high reproducibilities, and high chemoselectivities at 0 degrees C. Various isolation strategies of the sensitive products and their conversion to stable compounds. A set of synthetically versatile 2-aryl-2,3-epoxy-1-cyclohexanols and 1-aryl-6-hydroxy-1-cyclohexenes has been isolated and fully characterized.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | HAMMETT SUBSTITUENT CONSTANTS; SINGLET OXYGEN; ENE REACTION; MECHANISM; OLEFINS; REACTIVITY; DEPENDENCE; REDUCTION; CHEMISTRY; PRODUCTS; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Arbeitskreis Prof. Dr. Axel Jacobi von Wangelin |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 07 Apr 2020 05:21 |
| Last Modified: | 07 Apr 2020 05:21 |
| URI: | https://pred.uni-regensburg.de/id/eprint/26414 |
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