D. Sevenard, O. Kazakova, D. L. Chizhov
Feb 1, 2007
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0
Influential Citations
3
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Journal
Helvetica Chimica Acta
Abstract
The behavior of linear and cyclic fluorinated 1,3,5-triketones and their metal derivatives towards common halogenating agents was examined, and optimal reaction conditions for the straightforward syn- thesis of mono-, di-, and tetrahalogenated products were found (Schemes 1 - 3). An aromatization through a double HBr elimination from an a,a'-dibrominated cyclohexanone was shown to be a prom- ising synthetic route to 1,1'-(2-hydroxy-1,3-phenylene)bis(2,2,2-trifluoroethanones) (= 2,6-bis(trifluoro- A Scheme 4). Additionally, the 1,3,5-triketones prepared add readily H2O or alcohols to produce novel bridged 2,6-dihydroxypyran-4-ones (Scheme 2). The structure of the obtained compounds 6a and 7a was confirmed by X-ray structure analysis. Introduction. - Due to their polyfunctional nature and high reactivity, 1,3,5-trike- tones are versatile reaction partners in a variety of organic transformations (1), as well as valuable tridentate ligands in coordination chemistry (2). The methods of prep- aration and synthetic applications are well documented (1 - 3). However, little effort has been devoted to F-containing 1,3,5-triketones, although incorporation of F-atoms or fluorinated groups into organic compounds is known to induce dramatic consequen- ces on their chemical reactivity, physical properties, and biological activity (4). An excellent example of such a BtransformationC are fluorinated 1,3-dicarbonyl compounds. In this case, a significant change of the electron-density distribution results in peculiar tautomeric features (keto-enol, enol-enol) and in an unexpected behavior in the course of chemical reactions, when compared to nonfluorinated analogs (5). Continu- ing our long-standing interest in the chemistry of fluorinated 1,3-diketones and 1,3-keto esters (6), we have started a research program dealing with related 1,3,5-triketones (7). Given the synthetic importance of fluorinated 1,3-dicarbonyl compounds bearing an additional halogen atom in position 2 (8) (9), we have explored reactions of bis(trifluoroA triketones 1 and metal derivatives 2 with halogenating agents. The results obtained are presented herein. Results and Discussion. - In spite of advances in the halogenation of 3-(polyfluoro- Aed 1,3-keto esters (9), only scattered reports concerning related reac- tions of 1,3-diketones were published (10). Elemental Br2 was found to be unsuitable for selective bromination of 2-(trifluoroacetyl)cyclohexanone (10f) (11). On the other hand, N-bromosuccinimide (NBS) was efficient for the a-bromination of 4,4,4-tri-