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Reactions of Thioketones possessing a conjugated C=C bond with Diazo compounds


Egli, D H; Linden, A; Heimgartner, H (2006). Reactions of Thioketones possessing a conjugated C=C bond with Diazo compounds. Helvetica Chimica Acta, 89(12):3041-3055.

Abstract

The reactions of several thioketones containing a conjugated C=C bond with diazo compounds were investigated. All of the selected compounds reacted via a 1,3-dipolar cycloaddition with the C=S group and subsequent N2 elimination to yield thiocarbonyl ylides as intermediates, which underwent a 1,3-dipolar electrocyclization to give the corresponding thiirane 25, or, by a subsequent desulfurization, to give the olefins 33a and 33b. None of the intermediate thiocarbonyl ylides reacted via 1,5-dipolar electrocyclization.
If the a,b-unsaturated thiocarbonyl compound bears an amino group in the b-position, the reactions with diazo compounds led to the 2,5-dihydrothiophenes 40a–40d. In these cases, the proposed mechanism of the reactions led once more to the thiocarbonyl ylides 36 and thiiranes 38, respectively. The thiiranes reacted via an SNi’-like mechanism to give the corresponding thiolate/ammonium zwitterion 39, which underwent a ring closure to yield the 2,5-dihydrothiophenes 40. Also in these cases, no 1,5-
dipolar electrocyclization could be observed. The structures of several key products were established by X-ray crystallography.

Abstract

The reactions of several thioketones containing a conjugated C=C bond with diazo compounds were investigated. All of the selected compounds reacted via a 1,3-dipolar cycloaddition with the C=S group and subsequent N2 elimination to yield thiocarbonyl ylides as intermediates, which underwent a 1,3-dipolar electrocyclization to give the corresponding thiirane 25, or, by a subsequent desulfurization, to give the olefins 33a and 33b. None of the intermediate thiocarbonyl ylides reacted via 1,5-dipolar electrocyclization.
If the a,b-unsaturated thiocarbonyl compound bears an amino group in the b-position, the reactions with diazo compounds led to the 2,5-dihydrothiophenes 40a–40d. In these cases, the proposed mechanism of the reactions led once more to the thiocarbonyl ylides 36 and thiiranes 38, respectively. The thiiranes reacted via an SNi’-like mechanism to give the corresponding thiolate/ammonium zwitterion 39, which underwent a ring closure to yield the 2,5-dihydrothiophenes 40. Also in these cases, no 1,5-
dipolar electrocyclization could be observed. The structures of several key products were established by X-ray crystallography.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:2006
Deposited On:06 Dec 2011 07:29
Last Modified:05 Apr 2016 15:07
Publisher:Verlag Helvetica Chimica Acta
ISSN:0018-019X
Funders:Swiss National Science Foundation , F. Hoffmann-La Roche AG, Basel
Publisher DOI:https://doi.org/10.1002/hlca.200690274

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