FR2829490A1 - Conversion of 1,2-disubstituted epoxides to their alpha-diketone derivatives, useful as synthetic intermediates, involves oxidation in the presence of a bismuth salt - Google Patents

Abstract

Process for the direct transformation of a 1,2-disubstituted epoxide compound to its alpha-diketone derivative involves oxidation in the presence of a suitable amount of a bismuth salt and/or a compound able to generate it in situ, and a ring-opening activator. An Independent claim is also included for the compounds obtained by the process.

Description

<Desc / Clms Page number 1>

 The main subject of the present invention is a process useful for producing the opening of a 1,2-disubstituted, linear or cyclic epoxide ring and more particularly for converting such a ring directly into its α-diketone derivative.

 Epoxides are particularly interesting synthetic intermediates given the possibilities offered by the opening of their oxirane ring.

 In this case, depending on the oxidation conditions selected, it is possible to direct the opening of this cycle so as to access different compounds.

 Thus, the use of DMSO as an oxidant leads by acid catalysis directly to the formation of α-ketols or, in the presence of oxalyl chloride, to an α-chloroketone derivative.

 On the other hand, under different oxidation conditions, it is possible to break the carbon-carbon bond, in particular for the terminal epoxides, to form the carboxylic acids in the presence of Bi (III) / 02 'or the corresponding aldehydes and ketones in the presence of ammonium nitrate and cerium (IV).

 However, to date there are no examples of direct conversion of epoxides into α-diketone derivatives.

 In general, these α-diketone derivatives are obtained either by oxidation of vicinal diols, α-functionalized ketones or alkynes.

 In fact, these methods are not entirely satisfactory in that they often use salts, metal oxides or their derivatives, KMnO type, MnO2, CrOg, HgO, which generate embarrassing metal waste.

 It is clear that the synthesis of molecules for therapeutic or dietary purposes prohibits the use of certain metals insofar as the risk that these metals remain even in trace amounts in products intended to be present can not be excluded with certainty. consumed.

<Desc / Clms Page number 2>

 Finally, the use of such reagents does not always lead to a high selectivity at the level of the oxidation products. Thus, alkanes, oxidized by potassium permanganate on alumina, lead to a mixture of ketone and diketone. The latter being obtained with low yields.

 On the other hand, the treatment of olefins by various oxidizing systems leads preferentially to the monocetones.

 In this case, the object of the present invention is precisely to propose a new route of access to α-diketones via the opening of a 1,2-disubstituted epoxide ring.

 More specifically, the present invention is aimed primarily at a process for directly transforming a 1,2-disubstituted epoxide ring into its α-diketone derivative, characterized in that the said ring is oxidized in the presence of at least one effective amount of a bismuth salt and or any compound capable of generating it in situ and an activator for opening said cycle.

 The inventors have noted that the claimed process makes it possible to lead selectively to the conversion of the treated epoxide ring into its α-diketonic derivative. Advantageously, the reaction conditions retained in the context of the claimed process make it possible to avoid the phenomenon of overoxidation that might have been expected. The transformation carried out in the context of the invention is said to be direct in the sense that it is carried out in a single step.

 As for the active species of bismuth, it comprises at least one salt of bismuth lil.

 As an illustration of the salts that may be used in the context of the present invention, there may be mentioned those chosen from inorganic hydracid salts such as: chloride, bromide, iodide, sulphide, selenide, bismuth tellurium and the salts of aliphatic organic acids or

<Desc / Clms Page number 3>

 aromatics such as: acetate, propionate, benzoate, salicylate, oxalate, tartrate, lactate, citrate and bismuth mandelate.

The bismuth derivatives that are particularly suitable for the invention are: bismuth halides and more particularly bismuth chloride and bismuth mandelate Bi2O (C8H703) 4 '
As mentioned above, it is also conceivable to generate in situ this active species of bismuth from an organic derivative of bismuth or metal bismuth.

 According to a preferred embodiment of the invention, the bismuth salt is generated in situ within the reaction medium by oxidation of metal bismuth. This embodiment is particularly advantageous in terms of cost, insofar as it makes it possible to use a significantly reduced amount of bismuth atoms compared to a bismuth salt.

 The generation of the bismuth salt can in particular be visualized during the oxidation reaction through the progressive dissolution of the metal bismuth. This oxidation of the metal bismuth is preferably conducted using molecular oxygen or a gas containing it.

 In the case of a gas, it is of course chosen so that its other constituents remain inert during the oxidation reaction considered. It can also be air provided that it is free of any trace of moisture.

 As mentioned above, the amount of bismuth introduced varies according to whether said compound is used in the form of a metal or in the form of a salt in the oxidation state, such as, for example, in the form of bismuth mandelate. lil.

 In general, it is present at a rate of at most 55 mol% relative to the epoxide ring. However, when this bismuth salt is generated in situ from the metal bismuth, the latter is advantageously introduced in a proportion of 5 to 15% and preferably about 8 mol% relative to the epoxide ring.

<Desc / Clms Page number 4>

As regards more particularly the activator, it is generally selected from Lewis acids and protic acids. It is preferably a Lewis acid. It may especially be a metal salt, halide, perchlorate, ether, trifluoromethanesulfonate or triflate type, an alumina or zeolite.

Particularly suitable derivatives are selected from trifluoromethanesulfonic acid or triflic acid and metal salts of Mn + (ORF) -n or Mn + (NRF2) 'n with Mn + being an alkali metal, alkaline earth or transition and RF representing an atom halogen; a perhalogenated alkyl group optionally interrupted by an oxygen or sulfur atom; a radical selected from the radicals R-CF-, RACF2-CF2-, RA-CF2-CF (CFg) - and CF3-C (RA) F-, with RA being a hydrogen atom or an alkyl group. Advantageously, the halogens present are fluorine atoms and the perhalogenated chains, perfluorinated chains. As a representative and non-limiting example of these metal salts may be mentioned more specifically copper trifiate ii.

In the context of the present invention, it is advantageous to adjust the acidic strength of the activator as a function of the voltage of the epoxide ring 1, 2 disubstituted to be converted.

In this case, activators comparable to Lewis acids of acid strength assimilable to that of copper triflate II are more particularly advantageous for converting epoxides present in cyclic structures having at most 6 members.

On the other hand, in the case of epoxides present in a cyclic structure having more than 6 members, such as cyclododecene, or in a linear structure, the use of an activator having a higher acid strength and especially in the image of that triflic acid is more advantageous.

<Desc / Clms Page number 5>

 The activator may be used at 1 to 30 mol% and preferably at 2 to 25 mol% based on the epoxide ring.

 In fact this amount of activator is also likely to be adjusted depending on the acid strength of the activator considered.

 In this case, in the case of a so-called strong acid activator like triflic acid, it is advantageous not to exceed 3 moles of activator per bismuth atom.

 As regards the epoxidized substrate to be converted, it is a cyclic or linear 1,2-disubstituted epoxide ring.

dans laquelle : - R1 et R2 identiques ou différents, représentent : (1) un groupe alkyle ; (2) un groupe alcényle non conjugué avec l'époxyde ; (3) un groupe alcynyle non conjugué avec l'époxyde, à l'exception d'un groupe alcynyle présentant un groupement acétylénique vrai-C=C-H ; (4) un groupe aryle ; (5) un groupe arylalkyl (6) un groupe arylalcényle ; ou (7) un groupe arylalcynyle ; ou bien les deux groupements R1 et R2 sont liés entre eux de manière à former une chaîne hydrocarbonée, linéaire ou ramifiée, saturée ou insaturée. More preferably, this epoxide ring corresponds to the formula

in which: R1 and R2, which are identical or different, represent: (1) an alkyl group; (2) an alkenyl group unconjugated with the epoxide; (3) an alkynyl group unconjugated with the epoxide, with the exception of an alkynyl group having a true acetylenic group-C = CH; (4) an aryl group; (5) an arylalkyl group (6) an arylalkenyl group; or (7) an arylalkynyl group; or the two groups R1 and R2 are linked together so as to form a hydrocarbon chain, linear or branched, saturated or unsaturated.

 The general formula 1 covers, of course, the different stereochemical forms of the compounds under consideration.

<Desc / Clms Page number 6>

 Furthermore, in the context of the invention, it is meant to cover by the term "alkyl group" a linear or branched saturated hydrocarbon radical which may optionally include one or more saturated aliphatic ring (s). Within the meaning of the invention, the alkyl groups can have up to 25 carbon atoms. They preferably contain from 1 to 12 carbon atoms, and preferably from 1 to 6 carbon atoms. Thus, non-limiting examples of alkyl groups are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, 2-methylbutyl, 1-ethylpropyl, hexyl, isohexyl, neohexyl, 1-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,3-dimethylbutyl, 2-ethylbutyl, 1-methyl-1-ethylpropyl, heptyl, 1-methylhexyl, 1-propylbutyl, 4-dimethylpentyl, octyl, 1-methylheptyl, 2-ethylhexyl , 5,5-dimethylhexyl, nonyl, decyl, 1-methylnonyl, 3,7-dimethyloctyl and 7,7-dimethyloctyl.

 In particular, an alkyl group may also designate, within the meaning of the invention, a fused or unsuspended cycloalkyl group, that is to say a cyclic saturated hydrocarbon radical, preferably having from 3 to 10 carbon atoms, such as that, for example, cyclopentyl, cyclohexyl, cycloheptyl or cycloctyl.

 Moreover, the term "alkenyl group" as used herein means an unsaturated hydrocarbon radical, linear or branched, having at least one C = C double bond. The alkenyl groups of the invention can have up to 25 carbon atoms. They preferably comprise from 2 to 12 carbon atoms, and advantageously from 2 to 6 carbon atoms.

 Similarly, the term "alkynyl group" means an unsaturated hydrocarbon radical, linear or branched and having at least one C = C triple bond, it being understood that the triple (s) bond (s) present (s) do not part of a true CCH acetylenic group. The alkynyl groups of the invention may, as a rule, have up to 25 carbon atoms.

<Desc / Clms Page number 7>

 carbon, and they preferably comprise from 3 to 15 carbon atoms, and preferably from 3 to 6 carbon atoms.

 An "aryl" group is in the sense of the invention, a mono-or polycyclic aromatic group generally having from 5 to 20 carbon atoms, and preferably from 6 to 10 carbon atoms. Thus, it may for example be a phenyl group, or 1-or 2-naphthyl.

 According to one particular variant, an "aryl" group within the meaning of the invention can integrate one or more heteroatoms such as sulfur, oxygen, or nitrogen. In this particular case, the "aryl" group within the meaning of the invention denotes a mono- or polycyclic heteroaromatic group.

 The "arylalkyl", "arylalkenyl" and "arylalkynyl" groups within the meaning of the invention are alkyl, aryl or alkynyl chains substituted with an aryl group as defined above. In other words, these are Ar-Ra groups, where Ar represents an aryl group and Ra represents an alkylene, alkenylene or alkynylene chain. The "arylalkynyl" groups of the invention do not have true CCH acetylenic groups.

 The various alkyl, alkenyl, alkynyl, aryl, arylalkyl, arylalkenyl or arylalkynyl radicals present in the compounds used according to the invention may optionally be interrupted by heteroatoms or SO 2, SO 2 or amine groups. secondary or tertiary, or substituted by any type of groups not likely to interfere with the opening reaction of the epoxide ring implemented, and in particular by halogen atoms, or by silyl groups.

 With regard to the carbon chains mentioned in the definitions given in the present description, they are saturated or unsaturated chains which preferably contain from 3 to 15 carbon atoms, and which may also be substituted or incorporate heteroatoms or SO-type groups:, -, - SO-, or secondary or tertiary amines. Of course, in the general case, the choice of different heteroatoms present

<Desc / Clms Page number 8>

 is performed to ensure their non-interference in the opening reaction considered. This remark is also valid for the substituents which may be present, and more particularly as regards the amines or alcohols possibly present, which may advantageously be, if appropriate, in a protected form so as to guarantee their non-reactivity.

 Similarly, it should be emphasized that, irrespective of their exact nature, the R 1 and R 2 groups present in the compounds of formula (1) preferably used must be inert under the reaction conditions.

 All of these groups can be substituted with the proviso that the substituents remain inert during the transformation reaction.

It may especially be alkyl or alkenyl groups.

 The claimed process is particularly advantageous for preparing linear or branched aliphatic α-diketones, in particular in the form of 2,3-butanedione, 2,3-pentanedione, 2,3-hexanedione and 3,4-hexanedione.

 Likewise, it is advantageous for the oxidation of cyclic epoxides of general formula 1 in which R 1 and R 2 are linked together so as to form a linear or branched, saturated or unsaturated hydrocarbon-based chain. This hydrocarbon chain may also be part of a saturated or unsaturated hydrocarbon ring, condensed or not.

 It is understood that the α-diketones obtained according to the invention can be in the form of enol.

 Advantageously, the epoxy substrate is present in a cycle of 5 to 13, and preferably of 5.6 or 12 links.

 By way of illustration of this type of substrate, mention may be made more particularly of the compounds appearing in Table 1 below.

 According to a preferred embodiment of the invention, the substrate is brought together in a form solubilized with the bismuth salt and

<Desc / Clms Page number 9>

 the activator considered. In this way, the oxidation of the epoxide function in its α-diketone derivative is preferred and the manifestation of the polymerization of this substrate is prevented.

 The pre-solubilization and the subsequent conversion of the epoxide ring is generally conducted in a sufficiently polar solvent to allow the solubilization of the active species BI lil, generated or not in situ.

 According to a preferred embodiment of the invention, it is dimethylsulfoxide (DMSO) or the like, such as an aprotic polar solvent with a boiling point greater than 80 C combined, if necessary, with an oxygen transfer agent (example N-oxides).

 DMSO is particularly interesting for its simultaneous oxidative and polar properties.

 The reaction is carried out under anhydrous conditions and more generally in the absence of any trace of undesirable nucleophilic agent likely to affect the smooth running of the reaction. For this reason, the entire reaction medium is generally beforehand, purged with an inert gas before being placed under an oxygen atmosphere or a gas containing it. According to a preferred embodiment of the invention, the transformation is carried out at a temperature greater than room temperature, generally between 60 ° C. and 120 ° C. and preferably of the order of 100 ° C. It is of course adjusted to to favor the kinetics of reaction while preserving the stability of the reagents brought together as well as that of the α-diketone derivative formed during the reaction. Similarly, it is adjusted so as to prevent the manifestation of a polymerization of the substrate.

 The claimed method may in particular be composed of the following steps:

<Desc / Clms Page number 10>

 mixing the bismuth salt or metal bismuth with the activator in the solvent in question, preferably DMSO under an inert atmosphere, brought into contact with the whole with molecular oxygen or any gas containing it, heating the assembly at the reaction temperature, introduction into said medium of the epoxide ring in a solubilized form, preservation of the whole with stirring and heating until formation of the expected α-diketone derivative, and recovery of the α-diketone derivative.

 The diketone derivative is recovered and purified at the end of the reaction according to conventional techniques which are within the skill of those skilled in the art.

 The invention also extends to compounds obtainable by the claimed process.

 In this case, 4-ethenylcyclohexan-1,2-dione is also claimed within the scope of the invention.

 The examples given below are presented by way of non-limiting illustration of the present invention.

 EXAMPLE 1

Oxidation of cyclohexene oxide by the Bi / OJDtVtSO system in the presence of copper triflate

<Desc / Clms Page number 11>

 a) Bismuth reagents: commercial (Aldrich).

Cu (OTf) copper (II) triflate: handled under nitrogen flow.

 Dimethyl sulfoxide DMSO: distilled on CaH 2 and handled under a stream of nitrogen.

Cyclohexene oxide 1a: commercial (Aldrich), distilled before use. (b) Experimental protocol
In a two-necked Schlenk balloon equipped with a cap serum, the metal bismuth (83.6 mg, 0.4 mmol) and a magnetic bar are introduced. The balloon is plugged, purged three times, placed under a nitrogen atmosphere and then tared. The copper (II) triflate (45 mg, 0.125 mmol) is then introduced under a stream of nitrogen. The bicol is connected to a refrigerant surmounted by a three-way valve, connected to an oxygen balloon on the one hand, and a mechanical pump on the other hand. After introducing 15 ml of DMSO by syringe through the septum, the assembly is purged three times, each time compensating for the depression by the oxygen of the flask by means of the three-way valve. The mixture is then heated with stirring to 100 ° C. and maintained for 10 minutes. The cyclohexene oxide (490 mg, 5 mmol) solubilized in 5 ml of DMSO is then introduced by means of a syringe through the septum, and allowed to stir at this temperature for 2 hours. The consumption of the epoxide is monitored by VPC analysis of samples of aliquots of the solution, which also makes it possible to observe the appearance and disappearance of the 2-hydroxycyclohexanone intermediate, indicating the end of the reaction.

 The reaction crude is poured into 50 ml of saturated water of sodium chloride and extracted three times with 50 ml of diethyl ether. The organic phases are combined, dried over magnesium sulfate for 1 hour, and the solvent is evaporated on a rotary evaporator. The residue is a yellow oil containing cyclohexan-1,2-dione and the part of DMSO extracted.

<Desc / Clms Page number 12>

c) Purification and analyzes
The residue is purified by chromatography on silica gel using dichloromethane as eluent.

 Cyclohexan-1,2-dione 1b is characterized by GC-MS and proton NMR as compared to a commercial sample (Aldrich). The yield in 1b is 74% (414 mg, 3.7 mmol).

EXAMPLE 2
Oxidation of 4-nonene oxide by the Bi / 02 / DMSO system in the presence of triflic acid

4-nonene 4a oxide prepared by epoxidation of 4nonene is used. It is in the form of a mixture of two cis and trans isomers. The operating conditions used are those described in Example 1.

Nonan-4,5-dione 4b, characterized by GC-MS and proton NMR and carbon 13, is obtained by comparison with literature data.

The yield in 4b is 83%.

EXAMPLE 3
Oxidation of various 1,2-disubstituted epoxides.

 All the reactions are carried out in DMSO at 100 ° C. under atmospheric pressure of oxygen. In Table 1, the proportion of metal bismuth used relative to the substrate is specified, the nature of the additive used, namely copper triflate Cu (OTf) 2 called "A" or triflic acid TfOH said " B ", as well as their catalytic amounts

<Desc / Clms Page number 13>

 corresponding.

 In this table, the reaction times are also specified.

 This table also reflects the nature of the product obtained and the corresponding yield.

<Desc / Clms Page number 14>

TABLEAU 1

TABLE 1

<Tb>
<tb> Bi <SEP> (0) <SEP> Additivea <SEP> Time
<tb> Entry <SEP> Epoxide <SEP> Product <SEP> Yield
<tb> equiv. <SEP> (equiv.) <SEP> h
<tb>#O
####
<tb>#<SEP> O
<tb> 1a <SEP> 1b
<tb>#O
<tb> 2 <SEP>## O <SEP> 0.05 <SEP> A (0.08) <SEP> 1.3 <SEP>##<SEP> 77%
<tb>#O
<tb> 2a <SEP> 2b
<tb>#O
<tb> 3 <SEP>#O<SEP> 0.08 <SEP> A (0.06) <SEP> 2.3 <SEP>#SEP> 48%
<tb>#O
<tb> 3a <SEP> 3b
<tb> O <SEP> O <SEP> O
<tb> 4 <SEP>#<SEP> 0.10 <SEP> B (0.2) <SEP> 2.3 <SEP>#SEP> 83%
<tb> nPr <SEP> nBu <SEP> nPr # nBu
<tb> 4a <SEP> 4b
<tb>#O
<tb> 5 <SEP>## O <SEP> 0.06 <SEP> B (0.09) <SEP> 7.0 <SEP>#<SEP> 70%
<tb>#O
<tb> 5a <SEP> 5b
<tb>#O
<tb> 6 <SEP>#O<SEP> 0.06 <SEP> A (0.07) <SEP> 2 <SEP>#<SEP> 52%
<tb> 6a <SEP>#
<tb> O <SEP> 6b
<Tb>

From these results, it appears that all the epoxides leads to the corresponding alpha-diketones in good yields.

<Desc / Clms Page number 15>

Li (NTf2) ou l'acide protique TfOH. Ainsi, l'époxyde 1 a a été oxydé en 1, 2- cyclohexanedione 1b avec 74% de rendement (entrée 1). D'autre part, pour les cycles de taille supérieure (n=12,5a) ou pour les époxydes linéaires tel que 4a, la tension sur le cycle oxirane étant plus faible, l'utilisation de l'acide triflique TfOH à la place de Cu (OTf) 2 permet les meilleurs résultats (entrées 4,5). Le principal produit secondaire dans l'oxydation de 4a et 5a a été la monocétone correspondante, issue de l'isomérisation de l'époxyde en milieu acide. In the case of 5- or 6-membered cyclic epoxides (entries 1-3, 6), the use of Cu (OTf) 2 (2.5-8 mol%) as an additive led to the best results, compared with other Lewis acids such as BiCl3,

Li (NTf2) or protic acid TfOH. Thus, epoxide 1a was oxidized to 1,2-cyclohexanedione 1b with 74% yield (entry 1). On the other hand, for the larger size cycles (n = 12.5a) or for the linear epoxides such as 4a, the tension on the oxirane ring being lower, the use of triflic acid TfOH in place of Cu (OTf) 2 allows the best results (entries 4,5). The main secondary product in the oxidation of 4a and 5a was the corresponding monoketone, resulting from the isomerization of the epoxide in an acid medium.

 The oxidation of the unsaturated epoxides 2a and 3a indicates that the olefin functions are not modified by the system.

 The 5- and 6-membered cyclic α-diketones were mainly observed in their enolized form in proton NMR analysis (in CDCl3 at 20 ° C). Especially in the case of entry 3, only the 1,2-dihydroxybenzene form was observed. Similarly, the diketones 4b and 5b showed low enolization (respectively 36 and 30%) under the same analytical conditions.

EXAMPLE 4
The experimental conditions described in Example 1 are reproduced but using bismuth mandelate (!))), (Mand BiOBi (mand.

 In this particular case, cyclohexene oxide (490 mg, 5 mmol) is directly brought into contact with said salt (5 mol%) in DMSO (15 ml) and copper (II) triflate (6 mol%).

 The whole is heated with stirring to 100 C for three hours.

<Desc / Clms Page number 16>

 At the end of the opening reaction, the corresponding diketone is recovered according to the conditions described in Example 1. We obtain a total conversion.

 This test is also repeated on cyclooctene oxide with as bismuth salt bismuth trichloride (III) (50 mol%) and in the presence of copper (II) acetate (5 mol%). The whole is heated for 73 hours at 100 ° C. under an atmosphere of 0 ° C.

 A conversion of 80% is observed and the corresponding diketone is obtained with a yield of 32%.

Claims (23)

 1. A process for directly transforming a 1,2-disubstituted epoxide ring into its α-diketone derivative, characterized in that said ring is oxidized in the presence of at least one effective amount of a bismuth salt and / or any compound capable of generate it in situ and an activator for opening said cycle. 2. Method according to claim 1, characterized in that the active species of bismuth comprises at least one salt of bismuth lil. 3. Method according to claim 1 or 2 characterized in that the active species of bismuth is generated in situ from metal bismuth. 4. Method according to one of claims 1 to 3 characterized in that the amount of salt of bismuth or metal bismuth is adjusted so that the metal is present at a rate of at most 55 mol% relative to the epoxide ring 1,2 disubstituted. 5. Method according to claim 3, characterized in that the metal bismuth is used in a proportion of 5 to 15% and preferably 8 mol% relative to the 1,2-disubstituted epoxide ring. 6. Method according to one of claims 1 to 5, characterized in that the activator is a Lewis acid or a protic acid. 7. Process according to claim 6, characterized in that the Lewis acid is chosen from the metal salts of the halide, perchlorate, ether and trifiate type; umines and zeolites. 8. Process according to any one of the preceding claims, characterized in that the activator is preferably a derivative chosen from <Desc / Clms Page number 18>  triflic acid and metal salts of Mn + (ORF) -n or Mn + (NRF) type with Mn + being an alkali metal, alkaline earth metal or transition metal and RF representing a halogen atom, an optionally interrupted perhalogenated alkyl group; by an oxygen or sulfur atom, a radical chosen from the radicals RA-CF2-, RA-CF2-CF2-, RA-CF2-CF (CF3) - and CF3C (RA) F-, with RA representing an atom hydrogen or an alkyl group.  9. Process according to claim 8, characterized in that it is triflic acid or copper trifate II.  10. Method according to one of the preceding claims, characterized in that the activator is present in a proportion of 1 to 30 mol% relative to the epoxide ring.  11. Method according to one of the preceding claims, characterized in that the oxidation reaction is carried out under an oxygen atmosphere or a gas containing it.  12. Method according to one of the preceding claims, characterized in that the oxidation is carried out in an aprotic polar solvent with a boiling point greater than 80 C associated, if necessary, with an oxygen transfer agent.  13. Method according to one of the preceding claims, characterized in that the oxidation is carried out in DMSO.  14. Method according to one of the preceding claims, characterized in that the reaction is preferably carried out at a temperature between 60 and 120 C, and preferably of the order of 100 C.  15. Process according to one of the preceding claims, characterized in that the epoxide ring corresponds to the formula: <Desc / Clms Page number 19>  wherein: R, and R, which are identical or different, represent: (1) an alkyl group; (2) an alkenyl group unconjugated with the epoxide; (3) an alkynyl group not conjugated with the epoxide, except for an alkynyl group having a true acetylenic group - C = C-H; (4) an aryl group; (5) an arylalkyl group (6) an arylalkenyl group; or (7) an arylalkynyl group; or the two groups R1 and R2 are linked together so as to form a hydrocarbon chain, linear or branched, saturated or unsaturated.

 16. Method according to one of the preceding claims, characterized in that the epoxide ring is present in a linear or branched aliphatic hydrocarbon derivative.  17. Method according to one of claims 1 to 15, characterized in that the epoxide ring is present in a hydrocarbon ring of 5 to 13, and preferably of 5.6 or 12 links.  18. Method according to one of claims 1 to 15 and 17 characterized in that for the transformation of an epoxide ring present in a ring structure having at most 6 members is used as an activator acid acid lewis acid comparable to that of copper triflate ii. <Desc / Clms Page number 20>  19. Method according to one of claims 1 to 15 and 16 and 17 characterized in that for the transformation of an epoxide ring present in a ring structure having more than 6 members or in a linear structure, is used as a activator a strong acid activator and preferably triflic acid.  20. The method of claim 19 characterized in that the amount of bismuth is adjusted to at most 3 moles of a strong acid in the image of triflic acid per atom of bismuth.  21. Method according to one of the preceding claims characterized in that it comprises the steps of: - mixing the bismuth salt or metal bismuth with the activator in the solvent under an inert atmosphere; bringing said mixture into contact with molecular oxygen or a gas containing it; - warm the whole to the reaction temperature; introducing into said mixture the epoxide ring in a solubilized form; - Keep the whole stirring, and heating until formation of the expected α-diketone derivative; and isolating said α-diketone derivative.  22. Compound obtainable by the process as defined in claims 1 to 21.  23. Compound according to claim 22, characterized in that it is 4-ethenylcyclohexan-1,2-dione.