Technical field

The present invention relates to the field of organic synthesis and more specifically it concerns a process for preparing compound of formula (I) catalyzed by a Ruthenium complex.

Background

The bicyclic enol ether derivative of formula (I) is typical intermediate toward more valuable compound, such as saturated or unsaturated cyclic ketone. For examples, 16- oxabicyclo [10.3.1] hexadec- 12-ene or 14-methyl- 16- oxabicyclo [10.3.1] hexadec- 12- ene are key intermediates toward highly appreciated perfumery ingredients such as Exaltenone or Muscenone ^® (trademark from Firmenich SA). Said intermediates have been obtained since decades thanks to the direduction of a macrocyclic dione; e.g. 1,5- cyclopentadecanedione or 3-methylcyclopentadecane-l,5-dione, into the corresponding macrocyclic diol; e.g. 1,5-cyclopentadecanediol or 3-methylcyclopentadecane-l,5-diol, followed by dehydrogenation and dehydration to form a macrocyclic enol ether. The direct enol ether formation from the dione starting material has never been reported.

So there is still a need to develop such a more straightforward approach toward bicyclic enolether.

The present invention allows obtaining compound of formula (I) starting from cyclic diketone of formula (II) under transfer hydrogenation conditions using a secondary alcohol as a source of hydrogen.

Summary of the Invention

The invention relates to a novel process allowing the preparation of compound of formula (I) starting from compound of formula (II) while avoiding the formation and isolation step of the corresponding diol.

So, a first object of the present invention is a process for the preparation of a compound of formula (I) in a form of any one of its stereoisomers or a mixture thereof and wherein R represents a linear or branched Ci_ ₅ alkanediyl or alkenediyl group, optionally substituted by a phenyl group and R represents a linear or branched Ci_io alkanediyl or alkenediyl group, optionally substituted by a phenyl group;

comprising the reaction of a compound of the formula (II)

1 2

in a form of any one of its stereoisomers and wherein R and R have the same meaning as defined in formula (I);

with a ruthenium catalyst and in the presence of a base and a hydrogen source.

Description of the invention

Surprisingly, it has now been discovered that the compound of formula (I) can be produced in an advantageous manner by means of an one-pot reduction and cyclisation- dehydration type reaction of compound of formula (II) under transfer hydrogenation conditions. The invention's conditions allow avoiding the difficult handling of the corresponding diol and are highly selective toward monoreduction and lead to the formation of a bicyclic enol ether.

Therefore, a first object of the present invention is process for the preparation of a compound of formula (I)

in a form of any one of its stereoisomers or a mixture thereof and wherein R represents a linear or branched Ci_ ₅ alkanediyl or alkenediyl group, optionally substituted by a phenyl group and R represents a linear or branched Ci_io alkanediyl or alkenediyl group, optionally substituted by a phenyl group;

comprising the reaction of a compound of the formula (II)

1 2

in a form of any one of its stereoisomers and wherein R and R have the same meaning as defined in formula (I);

with a ruthenium catalyst and in the presence of a base and a hydrogen source.

According to any embodiments of the invention, and independently of the specific aspects, the compound (I) as well as the corresponding compound (II) can be in the form of any one of its stereoisomers or mixture thereof. For the sake of clarity by the term stereoisomer it is intended any diastereoisomer, enantiomer, racemate.

Indeed, the compound (I) or (II) may have at least one stereogenic center which can have different stereochemistry (i.e. when two stereogenic centers are present, compound (I) or (II) can have (R,R) or (R,S) configuration). Each of said stereogenic centers can be in a relative configuration R or S or a mixture thereof or in other words said compound of formula (II) or (I) can be in a form of pure enantiomer or diastereoisomer, or in a form of a mixture of stereoisomers.

According to any one of the above embodiments of the invention, said compounds of formula (II) are C7-C ₂₀ compounds.

According to any one of the above embodiments of the invention, compound (I) may be a compound of formul

in a form of any one of its stereoisomers and wherein R has the same meaning as defined in formula (I) and R represents a hydrogen atom or a methyl group.

According to any one of the above embodiments of the invention, compound (II) may be a compound of formula

in a form of any one of its stereoisomers and wherein R has the same meaning as defined in formula (I) and R represents a hydrogen atom or a methyl group.

According to any embodiments of the invention, R ¹ represents linear or branched Ci-5 alkanediyl or alkenediyl group optionally substituted by a phenyl group. Preferably, R ¹ represents a linear or branched Ci_ ₄ alkanediyl group. Preferably, R ¹ represents a linear or branched C ₂ -3 alkanediyl group. Even more preferably, R ¹ represents a 1 ,2-propanediyl group or a 1,2-ethanediyl group. Even more preferably, R ¹ represents a 1,2- propanediyl group.

According to any embodiments of the invention, R represents a linear or branched Ci_io alkanediyl or alkenediyl group group optionally substituted by a phenyl group. Preferably, R represents a linear or branched Ci- ₁₀ alkanediyl group. Preferably,

R represents a linear or branched C ₄ _9 alkanediyl group. Preferably, R represents a linear or branched C ₆ -9 alkanediyl group. Even more preferably, R represents a 1,8-octanediyl group.

According to any embodiments of the invention, R represents a hydrogen atom or a methyl group. Preferably, R may represent a methyl group.

Non-limiting examples of suitable compounds of formula (I) may include 12- oxabicyclo[6.3.1]dodec-8-ene, 10-methyl-12-oxabicyclo[6.3.1]dodec-8-ene, 13- oxabicyclo[7.3.1]tridec-9-ene, l l-methyl-13-oxabicyclo[7.3.1]tridec-9-ene, 14- oxabicyclo [8.3.1] tetradec- 10-ene, 12-methyl- 14-oxabicyclo [8.3.1] tetradec- 10-ene, 15- oxabicyclo[9.3.1]pentadec-l l-ene, 13-methyl-15-oxabicyclo[9.3.1]pentadec-l l-ene, 16- oxabicyclo [10.3.1 ]hexadec- 12-ene, 14-methyl- 16-oxabicyclo [10.3.1 ]hexadec- 12-ene, 17- oxabicyclo [11.3.1] heptadec- 13 -ene or 15 -methyl- 17- oxabicyclo [11.3.1] heptadec- 13 -ene . Preferably, the compound of formula (I) may be 16-oxabicyclo[10.3.1]hexadec-12-ene, 14-methyl- 16-oxabicyclo [10.3.1 ]hexadec- 12-ene, 17-oxabicyclo [11.3.1 ]heptadec- 13-ene or 15-methyl-17-oxabicyclo[11.3.1]heptadec-13-ene. Preferably, the compound of formula (I) may be 16-oxabicyclo[10.3.1]hexadec-12-ene or 14-methyl-16- oxabicyclo[10.3.1]hexadec-12-ene. Even more preferably, the compound of formula (I) may be 14-methyl-16-oxabicyclo[10.3.1]hexadec-12-ene.

Non-limiting examples of suitable compounds of formula (II) may include cycloundecane- 1 ,5-dione, 3-methylcycloundecane- 1 ,5-dione, cyclododecane- 1 ,5-dione, 3-methycyclododecane- 1 ,5-dione, cyclotridecane- 1 ,5-dione, 3-methycyclotridecane- 1 ,5- dione, cyclotetradecane- 1 ,5-dione, 3-methycyclotetradecane- 1 ,5-dione, cyclopentadecane- 1 ,5-dione, 3-methycyclopentadecane- 1 ,5-dione, cyclohexadecane- 1 ,5- dione or 3-methycyclohexadecane-l,5-dione . Preferably, the compound of formula (II) may be cyclopentadecane- 1,5-dione, 3-methycyclopentadecane- 1,5-dione, cyclohexadecane- 1, 5 -dione or 3-methycyclohexadecane- 1,5-dione. Preferably, the compound of formula (II) may be cyclopentadecane- 1,5-dione or 3- methycyclopentadecane- 1,5-dione. Even more preferably, the compound of formula (II) may be 3-methycyclopentadecane- 1,5-dione.

The compound of formula (II) is commercially available compound or can be prepared by several methods, such as the one reported in Helvetica Chimica Acta 1967, 56», 705, or in WO2016104474 or in WO2016184948.

According to any embodiments of the invention, the ruthenium catalyst is of formula

[Ru(X) ₂ P _n ] (III)

wherein X represents an anionic ligand; and when n is an integer between 1 to 4, P represents a monophosphine monodendate ligand; or when n is an integer between 1 to 2, P represents a biphosphine bidentate ligand.

According to any of the above embodiments of the invention, X represents an anionic ligand. A non-limiting list of anionic ligand includes a hydrogen or halogen atom, a hydroxy group, or an alkallyl, alkoxy or carboxylic radical.

By the term "alkallyl", it is meant the normal meaning in the art; i.e. a ligand comprising C=C-C ^" moiety.

According to any of the above embodiments of the invention, in formula (III), each X represents, simultaneously or independently, a hydrogen or chlorine or bromine atom, a hydroxy radical, or a Q to C ₆ alkallyl radical, such as a methallyl, a Q to C ₆ alkoxy radical, such as a methoxy, ethoxy or isopropoxy radical, or a Q to C ₆ carboxylic radical such as a HCOO, CH ₃ COO, CH ₃ CH ₂ COO or phenylCOO radical. Preferably, each X represents, simultaneously or independently, a chlorine or bromine atom, a methoxy, ethoxy or isopropoxy radical. Even more preferably, each X represents, simultaneously or independently, a chlorine or bromine atom.

According to any of the above embodiments of the invention, P represents a C ₃ - C70 mono-phosphine or a C ₆ -C6o biphosphine bidentate ligand. Preferably, P represents C ₃ -C ₃ o mono-phosphine, and in particular of formula PR ^d ₃ , wherein R ^d is a CrC ₁₂ linear, branched or cyclic alkyl, alkoxy or aryloxy group optionally substituted or a phenyl, diphenyl, furyl, pyridyl, naphthyl or di-naphthyl group optionally substituted; possible substituents being one or two halogen, hydroxy group, Ci to C ₁₀ alkoxy groups, halo- or perhalo-hydrocarbon, COOR, NR ₂ , quaternary amine or R groups, wherein R is a Ci to C ₆ alkyl, or a C5 to C ₁₂ cycloalkyl, arylkyl (such as benzyl, phenethyl etc..) or aromatic group, the latter being also optionally substituted by one, two or three halogen, sulfonates groups or Ci-Cg alkyl, alkoxy, amino, nitro, sulfonates, halo- or perhalo-hydrocarbon or ester groups. By "halo- or perhalo-hydrocarbon" it is meant groups such as CF ₃ or CC1H ₂ for instance. Even more preferably, R ^d is a phenyl, a tolyl a pyridyl or a furyl or a linear, branched or cyclic Ci_g alkyl group optionally substituted by a hydroxy or N(CH ₃ ) ₂ group. Even more preferably, P may represent a C ₃ -C ₇₀ mono-phosphine selected from the group consisting of triphenylphosphine, trimethylphosphine, triethylphosphine, tributylphosphine, tri-ie/t-butylphosphine, triccylohexylphosphine, tri-ortho- tolylphosphine, dimethylphenylphosphine, tri-2-furylphosphine, (4-(N^V- Dimethylamino)phenyl)di-iert-butyl phosphine, diphenyl-2-pyridylphosphine and tris(hydroxymethyl)phosphine. Even more preferably, P is triphenylphosphine.

Non-limiting examples of suitable ruthenium catalyst of formula (III) may include [Ru(H)(Cl)(PPh ₃ ) ₃ ], [Ru(H) ₂ (PPh ₃ ) ₃ ], [Ru(OAc) ₂ (PPh ₃ ) ₂ ], [Ru(OPiv) ₂ (PPh ₃ ) ₂ ], [Ru(Cl) ₂ (PBu ₃ ) ₃ ] .or [Ru(Cl) ₂ (PPh ₃ ) ₃ ] . Preferably, the ruthenium catalyst may be [Ru(Cl) ₂ (PPh ₃ ) ₃ ] .

The ruthenium catalyst can be added into the reaction medium of the invention' s process in a large range of concentrations. As non-limiting examples, one can cite as metal concentration values those ranging from 10 ppm to 200000 ppm, relative to the total amount of substrate. Preferably, the metal concentration will be comprised between 100 ppm to 10000 ppm, or even between 100 ppm and 500 ppm or 1000 ppm. It goes without saying that the process works also with more catalyst. However the optimum concentration of metal will depend, as the person skilled in the art knows, on the nature of the latter, on the nature of the substrate, on the temperature and on the desired time of reaction.

According to any embodiments of the invention, the invention process is performed in the presence of a base. Non-limiting examples of suitable base include tertiary amine, such as pyridine, trimethylamine, lutidine, N,N-Diisopropylethylamine or l,8-Diazabicyclo[5.4.0]undec-7-ene or alkali metal alkoxide, carboxylate, carbonate or hydroxide or a mixture thereof. Preferably, the base may be an alkali metal alkoxide, carboxylate, carbonate or hydroxide or a mixture of tertiary amine and alkali metal carbonate. Even more preferably, base may be an alkali metal carboxylate or carbonate or a mixture of tertiary amine and alkali metal carbonate. Even more preferably, base may be lithium, sodium or potassium acetate, ethanoate, propionate, butyrate, iert-butyrate, pentanoate or hexanoate.

The base can be added into the reaction medium of the invention's process in a large range of concentrations. As non-limiting examples, one can cite as base concentration values those ranging from 0.01 % to 100 % w/w, or even between 0.1 % to 5 % w/w, relative to the amount of compound of formula (II). It goes without saying that the optimum concentration of base will depend, as the person skilled in the art knows, on the nature of the latter, on the nature of the substrate, of the temperature and on the catalyst used during the process, as well as the desired time of reaction.

According to any one of the above embodiments of the invention, the hydrogen source is a hydrocarbon comprising at least one secondary alcohol functional group and having a boiling point equal or above to 110°C, preferably above 120°C. Said hydrogen source produces hydrogen while generating ketone. The hydrogen source may be a secondary alcohol. In particular the hydrogen source may be of formula

OH

JL (iv)

R ^R ⁵

wherein R ⁴ and R ⁵ , independently from each other, represent a Ci_io linear alkyl group optionally substituted by a hydroxy group or an aryl group, a C _2-1 o linear alkenyl group optionally substituted by a hydroxy group or an aryl group, a C ₃ _io branched or cyclic alkyl or alkenyl group optionally substituted by a hydroxy group or an aryl group, or a phenyl group optionally substituted by one to five C _1-3 alkyl or alkoxy groups, hydroxy groups or halogen atoms; or R ⁴ and R ⁵ , when taken together, represent a C _2-1 o linear or branched alkanediyl or alkenediyl optionally substituted by a hydroxy group or an aryl group. The hydrogen source of formula (IV) is a C ₄ _io compound.

The term "aryl group" designates the normal meaning in the art; i.e. an aromatic hydrocarbon group such as phenyl or naphthyl group optionally substituted. Non-limiting examples of the optional substituent of the aryl group may include C _1-3 alkyl or alkoxy group, a hydroxy group or a halogen atom.

According to any one of the above embodiments, R ⁴ may represent a Ci_io linear alkyl group optionally substituted by a hydroxy group or an aryl group or a C ₃ _io branched or cyclic alkyl group optionally substituted by a hydroxy group or an aryl group, or a phenyl group optionally substituted by one to five C _1-3 alkyl or alkoxy group, a hydroxy group or a halogen atom. Preferably, R ⁴ may represent a Ci_io linear alkyl group optionally substituted by a hydroxy group or a C ₃ _io branched or cyclic alkyl group optionally substituted by a hydroxy group. Preferably, R ⁴ may represent a C ₃ _8 linear or branched alkyl group optionally substituted by a hydroxy group. Even more preferably, R ⁴ may represent a methyl, ethyl, propyl, isopropyl, butyl, octyl group optionally substituted by a hydroxy group.

According to any one of the above embodiments, R ⁵ may represent a Ci_io linear alkyl group optionally substituted by a hydroxy group or an aryl group or a C _3-1 o branched or cyclic alkyl group optionally substituted by a hydroxy group or an aryl group. Preferably, R ⁵ may represent a methyl, an ethyl or a propyl group.

According to any one of the above embodiments, R ⁴ and R ⁵ , when taken together, may represent a C ₄ _ ₇ linear, branched alkanediyl or alkenediyl optionally substituted by a hydroxy group. Preferably, R ⁴ and R ⁵ , when taken together, may represent a C ₄ _ ₇ linear alkanediyl. Even more preferably, R ⁴ and R ⁵ , when taken together, may represent a C ₄ _ ₅ linear alkanediyl.

Non-limiting example of suitable hydrogen source may include 1-phenylethan- l- ol, 2-methyl-2,4-pentanediol, cyclohexanol, 4-methylpentan-2-ol, cyclopentanol or octan- 2-ol. Preferably, the hydrogen source may be 2-methyl-2,4-pentanediol, cyclopentanol, or 4-methylpentan-2-ol.

The hydrogen source can be added into the reaction medium of the invention's process in a large range of concentrations. As non-limiting examples, one can cite as hydrogen source concentration values those ranging from 1 equivalent to 50 equivalents, or even between 1 equivalent to 5 equivalents, relative to the amount of compound of formula (II). It goes without saying that the optimum concentration of hydrogen source will depend, as the person skilled in the art knows, on the nature of the latter, on the nature of the substrate, of the temperature and on the catalyst used during the process, as well as the desired time of reaction.

The invention's process is carried out under batch or continuous conditions.

The reaction can be carried out in the absence of a solvent.

The temperature of the invention's process may be comprised between 120°C and 300°C, more preferably in the range comprised between 150 °C and 250°C. Of course, a person skilled in the art is also able to select the preferred temperature as a function of the melting and boiling point of the hydrogen source and of the starting and final products as well as the desired time of reaction or conversion.

The invention's process may be performed under atmospheric pressure or under a slight vacuum. The invention's process may be performed under inert atmosphere such as nitrogen or argon.

According to any one of the above embodiments of the invention, the more volatile compounds generated during the invention's process are removed continuously during the invention's process. The removal of said more volatile compounds such as water and ketone formed during the invention process may be distillated during the invention process.

Examples

The invention will now be described in further details by way of the following examples, wherein the abbreviations have the usual meaning in the art, the temperatures are indicated in degrees centigrade (°C); the NMR spectral data were recorded in CDC1 ₃ (if not stated otherwise) with a 360 or 400 MHz machine for 1 H and 13 C, the chemical shifts δ are indicated in ppm with respect to TMS as standard, the coupling constants J are expressed in Hz.

Example 1

Preparation of compound of formula (I) starting from compound of formula (II)

In 11 glass reactor equipped with a mechanical stirrer, a packed column, a reflux condenser, 250g of 3-methyl-l,5-cyclopentadecanedione (0.99mol), a part or the totality of the hydrogen source (see Table 1), Ruthenium dichloro tris triphenylphosphine (0.92g, 0.00096mol), sodium propionate (0.96g, 0.0099mol) were loaded at atmospheric pressure or under vacuum (see Table 1). The mixture was stirred and heated to reflux (temperature depending on the nature of the solvent, see Table 1) while distilling into a flask the light fraction that was formed during the reaction (water and resulting ketone). After 22h, the reaction mixture was cooled to 100°C and the rest of the solvent was concentrated under vacuum. The residual oil (230g) was flash distilled (170°C, lmbar) and the distillate was analyzed by GC (see Table 1). Table 1 : Preparation of compound of formula (I) from compound of formula (II)

1) total loading at the beginning of the process.

2) pre loading of 20% of the total charge then addition of the rest over 16h.