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The [4+2]‐Cycloaddition of α‐Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero‐Diels–Alder Reactions—Experimental and Computational Studies


Mloston, Grzegorz; Urbaniak, Katarzyna; Jasinski, Marcin; Würthwein, Ernst-Ulrich; Heimgartner, Heinz; Zimmer, Reinhold; Reissig, Hans-Ulrich (2020). The [4+2]‐Cycloaddition of α‐Nitrosoalkenes with Thiochalcones as a Prototype of Periselective Hetero‐Diels–Alder Reactions—Experimental and Computational Studies. Chemistry - A European Journal, 26(1):237-248.

Abstract

The [4+2]-cycloadditions of alpha-nitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styryl-substituted 4H-1,5,2-oxathiazines in moderate to good yields. Of the eight conceivable hetero-Diels–Alder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the alpha-nitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bis-heterocyclic [4+2]-cycloadducts. The experiments are supported by high-level DFT calculations that were also extended to related hetero-Diels–Alder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2-dithiin and 2H-thiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process.

Abstract

The [4+2]-cycloadditions of alpha-nitrosoalkenes with thiochalcones occur with high selectivity at the thioketone moiety of the dienophile providing styryl-substituted 4H-1,5,2-oxathiazines in moderate to good yields. Of the eight conceivable hetero-Diels–Alder adducts only this isomer was observed, thus a prototype of a highly periselective and regioselective cycloaddition has been identified. Analysis of crude product mixtures revealed that the alpha-nitrosoalkene also adds competitively to the thioketone moiety of the thiochalcone dimer affording bis-heterocyclic [4+2]-cycloadducts. The experiments are supported by high-level DFT calculations that were also extended to related hetero-Diels–Alder reactions of other nitroso compounds and thioketones. These calculations reveal that the title cycloadditions are kinetically controlled processes confirming the role of thioketones as superdienophiles. The computational study was also applied to the experimentally studied thiochalcone dimerization, and showed that the 1,2-dithiin and 2H-thiopyran isomers are in equilibrium with the monomer. Again, the DFT calculations indicate kinetic control of this process.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2 January 2020
Deposited On:17 Dec 2019 14:27
Last Modified:03 Jan 2020 02:04
Publisher:Wiley-VCH Verlag
ISSN:0947-6539
OA Status:Green
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1002/chem.201903385

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