Technical field The present invention relates to the field of catalytic hydrogenation and, more particularly, to the use of a base-free catalytic system comprising a specific rhodium complex for the reduction of a conjugated dienal or dienone into the corresponding deconjugated enal or deconjugated enone. Background

The direct selective a-b hydrogenation, i.e. of a specific C=C bond, of a conjugated dienal (a,g-dienal) or conjugated dienone (a,g-dienone) is a challenging target. Indeed, the hydrogenation may take place at three different sites (two C=C and one C=0). Moreover, in order to render such process attracting for an industrial purpose, it is preferable to achieve the hydrogenation with an acceptable conversion and with a reasonable turn-over (complex load and reaction time).

The selective a-b reduction of conjugated dienals or conjugated dienones has been rarely reported in the literature. The selective a-b hydrogenation of conjugated dienals has been reported in W02012150053 wherein the selective hydrogenation is performed in the presence of a catalytic system comprising at least a base and at least one complex in the form of a rhodium complex comprising a C34-C60 bidentate diphosphine ligand (L2) coordinating the rhodium. However, the hydrogenations described in this prior arts are always carried out in a presence of a base which represents a drawback for certain substrates leading, in such conditions, to formation of polymer instead of the desired product. In addition, this prior is silent toward the selective a-b hydrogenation of dienones.

Therefore there is still a need for a base-free hydrogenation process allowing the selective a-b hydrogenation of a a,g-dienal or a,g-dienone, and if possible within reaction conditions which are applicable industrially. None of the prior art documents reports the use of the specific catalytic system comprising at least one Rh(I) complex obtainable by reacting a suitable Rh precursor having at least one CO ligand with a C34- C60 bidentate diphosphine ligand (L2) having a natural bite-angle comprised between 85° and 130° for the reduction of conjugated dienals or conjugated dienones.

Description of the invention

In order to overcome the problems aforementioned, the present invention relates to processes for the reduction by hydrogenation, i.e. using molecular ¾, of a C ₆ -C ₂₀ conjugated dienal or conjugated dienone into the corresponding deconjugated enal or deconjugated enone, characterized in that said process is carried out in the presence of a catalytic system comprising at least one complex in the form of a rhodium complex comprising a C ₃₄ -C ₆₀ bidentate diphosphine ligand (L2) coordinating the rhodium and at least one CO ligand.

According to a particular embodiment of the invention, the conjugated dienal or conjugated dienone is of formula wherein, when taken separately, each of R ¹ , R ² , R ³ , R ⁴ _, R ⁵ and R ⁶ represents, independently of each other, a hydrogen atom, a phenyl, Ci-8 alkyl, C _2-8 alkenyl, C _3-8 cycloalkyl or C _3-8 cycloalkenyl group, each optionally substituted, provided that at least one of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ is not a hydrogen atom; or R ¹ and R ² or R ² and R ³ or R ³ and R ⁴ , when taken together, represent a C _3-4 alkanediyl or alkenediyl group optionally substituted; or R ¹ and R ³ or R ² and R ⁵ , when taken together, represent a C _2-3 alkanediyl or alkenediyl group optionally substituted; or R ⁴ and R ⁵ , when taken together, represent a C _4-5 alkanediyl or alkenediyl group optionally substituted; or R ⁶ and R ¹ or R ⁶ and R ² , when taken together, represent a C _2-4 alkanediyl or alkenediyl group optionally substituted; or R ⁶ and R ⁵ , when taken together, represent a C _2-10 alkanediyl or alkenediyl group optionally substituted; into a deconjugated enal (when R ⁶ is a hydrogen atom) or deconjugated enone (when R ⁶ is not a hydrogen atom) of formula wherein R ¹ to R ⁶ have the same meaning as defined in formula (I); said process being carried out in the presence of a catalytic system comprising at least one Rh(I) complex obtainable by reacting a suitable Rh precursor having at least one CO ligand with a C34-C60 bidentate diphosphine ligand (L2) having a natural bite-angle comprised between 85° and 130°.

By the expression “natural bite-angle” it is understood the usual meaning in the art, e.g. as defined in P. W. N. M. van Leeuwen, P. C. J. Kamer, J. N. H. Reek, P. Dierkes, Chem. Rev. 2000, 2741. Possible substituents of R ¹ to R ⁶ are one phenyl group, one cyclohexyl, cyclopently, cyclohexenyl or cyclopentenyl group each optionally substituted by one, two or three C1-3 alkyl group, or one, two or three COOR ⁷ , OCOR ⁷ , N(R ⁷ )2, CN OR ⁸ or R ⁷ groups, wherein R ⁸ is a hydrogen atom or a R ⁷ group, wherein R ⁷ represents a C1-4 linear or branched alkyl or alkenyl group. Particularly, possible substituents of R ¹ to R ⁶ are one phenyl group, or one, two or three COOR ⁷ , OR ⁸ or R ⁷ groups wherein R ⁷ and R ⁸ have the same meaning as defined above. According to any one of the embodiments of the invention, only one or two of said R ¹ to R ⁶ may be optionally substituted, particularly, one or two of said R ¹ to R ⁵ may be optionally substituted .

The wavy line indicates that the double bond may be in the form of its E or Z isomer or of a mixture thereof; e.g. the C6-C20 conjugated dienal or conjugated dienone of formula (I) may be in a form of a composition of matter consisting of one or more compounds of formula (I), having the same chemical structure but differing by the configuration of the double bond. In particular, compound (I) comprises two double bond which can be each Z, E or a mixture thereof and compound of formula (II) comprises one double bond which can be Z, E or a mixture thereof. Compound of formula (I) and compound of formula (II) can be in the form of a mixture consisting of isomers E and Z and wherein said isomers E represent at least 50 % of the total mixture, or even at least 75% (i.e a mixture E/Z comprised between 75/25 and 100/0). For the sake of clarity, by the expression “R ¹ and R ² . , when taken together, represent a C _3-4 alkanediyl or alkenediyl group” or similar, it is meant the normal meaning understood by a person skilled in the art, i.e. a divalent group formed from alkane or alkene by removal of two hydrogen atoms. In other words, R ¹ and R ² , when taken together, form a C _5-6 cycloalkyl or cycloalkenyl group.

It is understood that said compounds (II) can be in a racemic or optically active form, depending on the nature of the substrate and on the complex used.

It is understood that by “alkenyl”, “cycloalkenyl” or “alkenediyl” group it is meant here the usual meaning in the art, which is an unsaturated group wherein the unsaturation cannot be conjugated to the carbon-carbon double bonds of the conjugated dienal or conjugated dienone.

The terms “alkyl” and “alkenyl” are understood as comprising branched and linear alkyl and alkenyl groups.

It is understood that by ’’conjugated dienal”, it is meant a compound possessing at least two carbon-carbon double bonds and an aldehyde functional group, the three of them being conjugated, as indicated in formula (I). The term ’’conjugated dienal” is therefore understood as optionally comprising also compounds having additional non aromatic carbon-carbon double bonds provided that said additional carbon-carbon double bonds are not conjugated to the ones of the dienal system. It is understood that by ’’conjugated dienone” or it is meant a compound possessing at least two carbon-carbon double bonds and a ketone functional group, the three of them being conjugated, as indicated in formula (I). The term ’’conjugated dienone” is therefore understood as optionally comprising also compounds having additional non-aromatic carbon-carbon double bonds provided that said additional carbon-carbon double bonds are not conjugated to the ones of the dienal system.

It is understood that by ’’deconjugated enal” it is meant a compound possessing at least one g-d carbon-carbon double bond and an aldehyde functional group, as indicated in formula (II). The term ’’deconjugated enal” is therefore understood as optionally comprising also compounds having additional carbon-carbon double bonds provided that said additional non-aromatic carbon-carbon double bonds are not conjugated to the one of the enal system. It is understood that by ’’deconjugated enone” it is meant a compound possessing at least one g-d carbon-carbon double bond and a ketone functional group, as indicated in formula (II). The term ’’deconjugated enone” is therefore understood as optionally comprising also compounds having additional carbon-carbon double bonds provided that said additional non-aromatic carbon-carbon double bonds are not conjugated to the one of the enone system.

According to any embodiments of the invention, the compounds of formula (I) and (II) is a C ₆ -C ₁₅ compound.

According to any embodiments of the invention, when taken separately, each of R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ represents, independently of each other, a hydrogen atom, a phenyl, Ci-6 alkyl, C5-6 cycloalkyl or C5-6 cycloalkenyl group, each optionally substituted, provided that at least one of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ is not a hydrogen atom; R ³ and R ⁴ , when taken together, represent a C _3-4 alkanediyl group optionally substituted; R ⁴ and R ⁵ , when taken together, represent a C _4-5 alkanediyl group optionally substituted. Particularly, when taken separately, each of R ¹ , R ² , R ³ , R ⁴ , R ⁵ and R ⁶ represents, independently of each other, a hydrogen atom, a phenyl, C _1-4 alkyl, C _5-6 cycloalkyl or C _5-6 cycloalkenyl group, each optionally substituted, provided that at least one of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ is not a hydrogen atom; R ³ and R ⁴ , when taken together, represent a C _3-4 alkanediyl group optionally substituted; R ⁴ and R ⁵ , when taken together, represent a C _4-5 alkanediyl group optionally substituted.

According to any embodiments of the invention, the compounds of formula (I) and (II) are respectively a conjugated dienone and a deconjugated enone; i.e. R ⁶ may be a phenyl, Ci-8 alkyl, C _2-8 alkenyl, C _3-8 cycloalkyl or C _3-8 cycloalkenyl group, each optionally.

According to any one of the above embodiments, when taken separately, said R ¹ may represent a hydrogen atom or a C _1-4 alkyl group. Particularly, R ¹ may represent a hydrogen atom or a C _1-3 alkyl group. Particularly, said R ¹ may represent a hydrogen atom, a methyl or a ethyl group. Even more particularly, said R ¹ may represent a hydrogen atom.

According to any one of the above embodiments, when taken separately, said R ⁶ may represent a hydrogen atom, a C _1-4 alkyl or phenyl group. Particularly, R ⁶ may represent a hydrogen atom, a C _1-3 alkyl group or a phenyl group. Particularly, said R ⁶ may represent a hydrogen atom, a methyl, ethyl or phenyl group. Even more particularly, R ⁶ may be a methyl or ethyl group.

According to any one of the above embodiments, when taken separately, said R ² may represent a hydrogen atom or a C _1-4 alkyl group. Particularly, R ² may represent a hydrogen atom or a C _1-3 alkyl group. Particularly, said R ² may represent a hydrogen atom, a methyl or a ethyl group. Even more particularly, said R ² may represent a hydrogen atom.

According to any one of the above embodiments, when taken separately, said R ³ may represent a hydrogen atom, a C _1-4 alkyl group or a phenyl group optionally substituted. Particularly, R ³ may represent a hydrogen atom, a C _1-3 alkyl group or a phenyl group. Particularly, said R ³ may represent a hydrogen atom, a methyl or ethyl group or a phenyl group optionally substituted.

According to any one of the above embodiments, when taken separately, said R ⁴ may represent a hydrogen atom, a methyl, ethyl, cyclohexyl, cyclohexenyl cyclopentyl, cyclopentenyl or phenyl group, wherein the cyclohexyl, cyclohexenyl cyclopentyl, cyclopentenyl or phenyl group may be each optionally substituted.

According to any one of the above embodiments, when taken separately, said R ⁵ may represent a hydrogen atom, a methyl, ethyl, cyclohexyl, cyclohexenyl cyclopentyl, cyclopentenyl or phenyl group, wherein the cyclohexyl, cyclohexenyl cyclopentyl, cyclopentenyl or phenyl group may be each optionally substituted.

According to any one of the above embodiments, when taken together, said R ³ and R ⁴ , when taken together, represent a C ₄ alkanediyl group optionally substituted.

According to any one of the above embodiments, when taken together, said R ⁴ and R ⁵ , when taken together, represent a C ₅ alkanediyl group optionally substituted.

According to any one of the above embodiments, the substrate of formula (I) may be one wherein R ¹ , R ² represent each a hydrogen atom, R ³ , R ⁴ , R ⁵ may represent each a hydrogen atom or a methyl, ethyl, cyclohexyl or phenyl group, wherein the cyclohexyl or phenyl group may be each optionally substituted, provided that at least one of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ is not a hydrogen atom; or R ³ and R ⁴ , when taken together, represent a C ₄ alkanediyl group optionally substituted.

According to any one of the above embodiments, the substrate of formula (I) may be one wherein at least one or two of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ may be a hydrogen atom.

According to any one of the above embodiments, the substrate of formula (I) may be one wherein two or three of said R ¹ , R ² , R ³ , R ⁴ and R ⁵ may be a hydrogen atom.

According to any one of the above embodiments, the substituents of said R ¹ to R ⁶ may be one phenyl group or one, two or three OR ⁸ or R ⁷ groups, in which R ⁸ is a hydrogen atom or a R ⁷ group, R ⁷ representing a C _1-4 linear or branched alkyl group. Preferably said substituents may be a OR ⁷ or R ⁷ group. According to any one of the embodiments of the invention, only one or two of said R ¹ to R ⁵ may be optionally substituted. Particularly, R ⁷ may represent a C1-3 alkyl group. Particularly, said R ⁷ may represent a methyl or a ethyl group.

According to a further embodiment of the invention, the substrate may be a conjugated dienal or a conjugated dienone that will provide a deconjugated enal or deconjugated enone that may be useful in the pharmaceutical, agrochemical or perfumery industry as final product or as an intermediate. Particularly preferred substrate may be a conjugated dienal or a conjugated dienone that will provide a deconjugated enal or deconjugated enone which may be useful in the perfumery industry as final product or as an intermediate.

Non-limiting examples of substrates are the following: (3E,5E)-5-methyl-6-(p- tolyl)hexa-3,5-dien-2-one, (3E,5Z)-5-phenylhepta-3,5-dien-2-one, (3E)-5-methylocta-3,5- dien-2-one, (3E)-5-ethylnona-3,5-dien-2-one, (3E)-5-propyldeca-3,5-dien-2-one, (3E,5E)- 6-cyclopentyl-5-methylhexa-3,5-dien-2-one, (3E,5E)-6-cyclohexyl-5-methylhexa-3,5- dien-2-one, (3E,5E)-5-(cyclohexylmethylene)hept-3-en-2-one, (E)-4-(5,5- dimethylcyclohex- 1 -en- 1 -yl)but-3-en-2-one, (E)-4-(2,6,6-trimethylcyclohex- 1 -en- 1- yl)but-3-en-2-one, (3E,5E)-6-(cyclohex-3-en-l-yl)-5-methylhexa-3,5-dien-2-one,

(3E,5E)-5-methyl-7-(2,6,6-trimethylcyclohex-l-en-l-yl)hep ta-3,5-dien-2-one, (3E,5E)-5- ethyl-7-((S)-2,2,3-trimethylcyclopent-3-en-l-yl)hepta-3,5-di en-2-one, 6-cyclohexylhepta- 3,5-dien-2-one, 6,10-dimethylundeca-3,5,9-trien-2-one, (3E,5E)-6-phenylhexa-3,5-dien- 2-one, (2£ ^' ,4£ ^' )-4-methyl-5-( -tolyl)penta-2,4-dienal, (2£',4£')-5-phenylpenta-2,4-dienal, (2£',4£)-5-phenylhexa-2,4-dienal, (2£',4£')-4-methyl-5-phenylpenta-2,4-dienal, (2E,AE)-2- methyl-5-phenylpenta-2,4-dienal, (2£',4Z)-4-phenylhexa-2,4-dienal, (£)-3-(4-(tert- butyl)cyclohex-l-en-l-yl)acrylaldehyde, (2E,4E)-5-cyclohexyl-4-methylpenta-2,4-dienal, (2E,4E)-5,9-dimethyldeca-2,4,8-trienal, 5,9-dimethyldeca-2,4-dienal, (2E,4E)-5- cyclopentyl-4-methylpenta-2,4-dienal, 5-methyl-7-phenylhepta-2,4-dienal, (E)-3-(5,5- dimethylcyclohex- 1 -en- 1 -yljacrylaldehyde or (2E)-4-methyldodeca-2,4-dienal.

According to a particular aspect of any one of the invention’s embodiments, the invention’s process is also characterized by providing compound (II) with a selectivity above 40%, particularly above 60%, particularly above 80%, particularly above 90%, more particularly above 95%. According to a particular aspect of any one of the invention’s embodiments, the invention’s process is also characterized by providing compound (II) with a conversion of the staring compound of above 60%, particularly above 70%, particularly above 80%, particularly above 90%, more particularly above 95%.

Wherein by “deconjugated enal” it is meant the compound (II), by “aldehyde” it is meant the compound (I) wherein both carbon-carbon double bonds have been reduced and by “alcohol” it is meant the aldehyde wherein the carbonyl has also been reduced. Wherein by “deconjugated enone” it is meant the compound (II), by “ketone” it is meant the compound (I) wherein both carbon-carbon double bonds have been reduced.

The hydrogenation reaction can be carried out in the presence or absence of a solvent. In a particular embodiment of the invention, the process is carried out in the presence of a solvent (in general for practical reasons), and any solvent current in hydrogenation reactions can be used for the purposes of the invention. Non-limiting examples include Ce-io aromatic solvents such as toluene or xylene, C1-2 halogenated hydrocarbon such as CH2CI2, C5-8 hydrocarbon solvents such as hexane or cyclohexane, C4-9 ethers such as tetrahydrofuran or MTBE, C3-9 esters such as ethyl or methyl acetate, C3-6 ketones such as acetone, polar solvents such as C1-5 primary or secondary alcohols such as isopropanol or ethanol, or mixtures thereof. The choice of the solvent is a function of the nature of the substrate and of the complex and the person skilled in the art is well able to select the most convenient solvent in each case to optimize the hydrogenation reaction.

In the hydrogenation process of the invention, the reaction can be carried out under an atmosphere of pure ¾ or under a mixture of hydrogen and of at least an inert gas, such as N2 or Ar. Preferably, the atmosphere of the reaction medium is CO-free, e.g. the amount of CO present is below 1 ppm. It is understood that in any case the reaction medium is preferably supplied with at least a steochiometric amount of H2 relative to the substrate; if less than a steochiometric amount of ¾ then it is achieved only a partial conversion of the substrate. In any case, as non-limiting example, one may cite typical ¾ pressure comprised between 10 ⁵ Pa and 80 x 10 ⁵ Pa (1 to 80 bar) or even more if desired. Again, a person skilled in the art is well able to adjust the pressure as a function of the complex load and of the dilution of the substrate in the solvent. As examples, one can cite typical pressures of 3 to 50 x 10 ⁵ Pa (3 to 50 bar), or even of 5 to 20 x 10 ⁵ Pa (5 to 20 bar). The temperature at which the hydrogenation can be carried out is comprised between 20°C and 100°C, preferably in the range of between 25°C and 80°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 starting and final products as well as the desired time of reaction or conversion.

According to any embodiment of the invention, the process of the invention is performed in absence of base.

As mentioned above, the present invention requires the use of a particular catalytic system comprising at least one Rh(I) complex obtainable by reacting a suitable Rh(I) precursor having at least one CO ligand with a C34-C60 bidentate diphosphine ligand (L2) having a natural bite-angle comprised between 85° and 130°

According to any one of the above embodiments, the Rh(I) complex is a compound obtainable by reacting together: a C34-C60 bidentate diphosphine ligand (L2) having a natural bite-angle comprised between 85° and 130°; and a suitable Rh precursor of formula

Rhp(CO) _q (Z)r (1) or RhH(CO)(P) ₃ (G) wherein p is an integer between 1 and 4; q is an integer between 2 and 20; r is an integer between 0 and 1; Z is a coordinated anion and P is a C3-C30 mono-phosphine.

According to any one of the above embodiments, Z may be a coordinated anion provided that Z is not an halide. Particularly, Z may be selected from the group consisting of acetylacetonate, l,l,l,5,5,5-hexafluoropentane-2,4-dionate, 2, 2,6,6- tetramethylheptane-3,5-dionate, a carboxylate such benzoate, acetate, formiate, pivalate or propionate, an alkoxide such as methoxide, ethoxide, propoxide or butoxide, an allyl such as prop-2-en-l-ide, 3-phenyl-prop-2-en-l-ide, a cyclopentadienyl, a pentamethylcyclopentadienyl and a pentafluorocyclopentadienyl. Particularly, Z may be acetylacetonate.

According to any embodiment of the present invention, P may represent a mono phosphine of formula PR ⁹ ₃ , wherein R ⁹ is a C1-C12 group, such as linear, branched or cyclic alkyl, alkoxy or aryloxy group optionally substituted, substituted or unsubstituted phenyl, diphenyl or naphthyl or di-naphthyl group. More particularly R ⁹ may represent a substituted or unsubstituted phenyl, diphenyl or naphthyl or di-naphthyl group. Possible substituents are those cited below for the group R ^b . Preferably, P is a triphenylphosphine. According to any embodiment of the present invention, the Rh(0) precursor of formula (1) or ( ) may selected from the group consisting of Rh(CO)2(acac), RhH(CO)(PPh ₃ ) ₃ , Rh4(CO)i2 and Rh ₆ (CO)i ₆ .

The preparation of the Rh(I) complex is preferably carried out in the presence of a solvent. In a particular embodiment of the invention, said solvent is the same optionally used in the hydrogenation process. However other solvents can be used, and as non limiting examples one may cite Ce-io aromatic solvents such as toluene or xylene, C5-8 hydrocarbon solvents such as hexane or cyclohexane, C4-9 ethers such as tetrahydrofuran or MTBE, polar solvents such as C1-5 primary or secondary alcohols such as isopropanol or ethanol, dichloromethane, water or mixtures thereof. The choice of the solvent is a function of the nature of the substrate and of the complex and the person skilled in the art is well able to select the most convenient solvent in each case to optimize the hydrogenation reaction.

The preparation of the Rh(I) complex can be carried out under an inert, or an essentially carbon monoxide and oxygen free atmosphere, e.g. the amount of CO and O2 present is below 1 ppm. A person skilled in the art knows what is meant by an inert atmosphere. Non-limiting examples of such atmosphere are a nitrogen or argon atmosphere.

In the preparation of the Rh(I) complex, the temperature of the process can be comprised between 0°C and 100°C, preferably in the range of between 10°C and 60°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 starting and final products as well as the desired time of reaction or conversion.

According to a particular embodiment, it is believed that the Rh(I) complex can be described as having the formula

[Rh(L2)(CO)(Z)] (2) wherein L2 and Z has the same meaning as defined above.

According to any one of the above embodiments, L2 can be a compound of formula

(R ^b ) ₂ P— Q— P(R ^b ) ₂ (A) wherein each R ^b , taken separately, represents a Ce-io aromatic group optionally substituted or a cyclohexyl group optionally substituted, or the two R ^b bonded to the same P atom, taken together, represent a 2,2'-oxydiphenyl optionally substituted; and Q represents a C10-C16 metallocenediyl optionally substituted or a group of formula - a) wherein each R ^d represents a hydrogen atom or a Ci- ₈ alkyl group, and X represents an oxygen or sulfur atom or a C(R ¹⁰ )2, Si(R ⁿ )2 or NR ¹⁰ group, in which R ¹⁰ is a hydrogen atom or a R ¹¹ group, R ¹¹ representing a C1-4 linear or branched alkyl group, preferably a methyl group; or - b) in the form of any one of its enantiomers, and wherein m is 0 or 1, M represents Fe or Ru, and R ^a represents a hydrogen atom or a C1-4 alkyl group; and the wavy lines indicate the position of the bond between said Q group and the rest of the compound (A).

According to any one of the above embodiments, Q represents a l,l’-ferrocenediyl optionally substituted or a group of formula - a) wherein each R ^d represents a hydrogen atom or a Ci-4 alkyl group, and X represents a C(R ¹⁰ ) ₂ , Si(R ⁿ )2 or NR ¹⁰ group, in which R ¹⁰ is a hydrogen atom or a R ¹¹ group, R ¹¹ representing a Ci-4 linear or branched alkyl group, preferably a methyl group; or b) in the form of any one of its enantiomers; the wavy lines indicate the position of the bond between said Q group and the rest of the compound (A).

According to any one of the above embodiments, in the definition of Q the metallocenediyl is a ferrocenediyl and in particular a 1,1’ -diyl group. In formula (ii), in particular, M is Fe.

According to any one of the above embodiments, each R ^b represents a Ce-io aromatic group optionally substituted or a cyclohexyl group optionally substituted.

According to any one of the above embodiments, by “aromatic group or ring” it is meant a phenyl or naphthyl group, and in particular a phenyl group.

According to any one of the above embodiments, each R ^b represents a phenyl group, a cyclohexyl group, a 3,5-dimethyl-phenyl, a 3,5-di(CF ₃ )-phenyl, a 3,5-dimethyl- 4-methoxy-phenyl group.

According to any one of the above embodiments, the R ^d represents a hydrogen atom.

According to any one of the above embodiments, X represents a CMe2, SiMe2, NH or NMe group. According to any one of the above embodiments, L2 has a natural bite- angle comprised between 93° and 125°, particularly, comprised between 97° and 125°, particularly comprised between 102° and 125°, particularly comprised between 108° and 125°, even more particularly, comprised between 110° and 125°. According to any one of the above embodiments, non-limiting examples of possible substituents of R ^b are one, two, three or four groups selected amongst the halogen atoms, or Ci-io alkoxy, alkyl, alkenyl, or perhalo-hydrocarbon groups. The expression “perhalo-hydrocarbon” has here the usual meaning in the art, e.g. a group such as CF3 for instance. In particular said substituents are one or two halogen atoms, such as F or Cl, or C1-4 alkoxy or alkyl groups, or CF3 groups.

According to any one of the above embodiments, non-limiting examples of possible substituents of the metallocenediyl or l,l’-ferrocenediyl group are one or two Ci- ₄ alkyl groups or a CR ^d PhN(R ^d ) ₂ group, wherein R ^d or R ^d are a hydrogen atom or a Ci- ₄ alkyl group and Ph is a phenyl group optionally substituted as indicated above for R ^b . In particular, said substituents are one methyl or one CH(C6H5)N(Me)2 group.

According to any one of the above embodiments, said R ^b metallocenediyl or 1,1’- ferrocenediyl groups, one by one or all together, are non-substituted.

According to any one of the above embodiments, the ligand of formula (A) can be in a racemic or optically active form.

As non- limiting examples of L2 ligands, one can cite the following ones:

(99°) (102°C) (103.7°) wherein Cy represents a cyclohexyl substituted by one or two Ci-4 alkyl groups, Ph represents a phenyl group optionally substituted by one or two C _I alkyl groups, one or two trifluoromethyl groups or by one methoxy group; said compounds being in an optically active form or in a racemic form, if applicable.

The ligands (A) are all known in the prior art and can be obtained by applying standard general methods which are well known in the state of the art and by the person skilled in the art, e.g. see R. P. J. Bronger, P. C. J. Kamer, P. W. N. M. van Leeuwen, Organometallics 2003, 22, 5358 or R. P. J. Bronger, J. P. Bermon, J. Herwig, P. C. J. Kamer, P. W. N. M. van Leeuwen, Adv. Synth. Catal. 2004, 346, 789 or M. Kranenburg, Y. E. M. van der Burgt, P. C. J. Kamer, P. W. N. M. van Leeuwen, K. Goubitz, J. Fraanje Organometallics 1985, 14, 3081 or P. Dierkes, P. W. N. M. van Leeuwen J. Chem. Soc., Dalton Trans. 1999, 1519. Some of said ligands are even commercially available. According to any one of the above embodiments, L2 ligand is selected from the group consisting of (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane) and 4,6- bis(diphenylphosphaneyl)-10H-phenoxazine.

In general, the complexes of formula (2) can be prepared and isolated prior to their use in the process according to the general methods described in the literature. A method is described in the Example.

Moreover, the complexes can be prepared in situ, by several methods, in the hydrogenation medium, without isolation or purification, just before their use.

The Rh complex of the invention 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 complex concentration amounts of complex being greater than 10 ppm, preferably greater than 100 ppm, more preferably greater than 1000 ppm, but less than 50000 ppm, preferably less than 10000 ppm, relative to the amount of substrate. It goes without saying that the optimum concentration of complex will depend, as the person skilled in the art knows, on the nature of the latter, on the nature of the substrate, of the solvent and on the pressure of ¾ used during the process, as well as the desired time of reaction.

Examples

The invention will now be described in further detail by way of the following examples, wherein the abbreviations have the usual meaning in the art, the temperatures are indicated in degrees centigrade (°C). NMR spectra were acquired using either a Bruker Avance II Ultrashield 400 plus operating at 400 MHz, ( ¹ H) and 100 MHz ( ¹³ C) or a Bruker Avance III 500 operating at 500 MHz ( ¹ H) and 125 MHz ( ¹³ C) or a Bruker Avance III 600 cryoprobe operating at 600 MHz ( ¹ H) and 150 MHz ( ¹³ C). Spectra were internally referenced relative to tetramethyl silane 0.0 ppm. ¹ H NMR signal shifts are expressed in d ppm, coupling constants ( J) are expressed in Hz with the following multiplicities: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; b, broad (indicating unresolved couplings) and were interpreted using Bruker Topspin software. ¹³ C NMR data are expressed in chemical shift d ppm and hybridization from DEPT 90 and DEPT 135 experiments, C, quaternary (s); CH, methine (d); CH ₂ , methylene (t); CH ₃ , methyl

(q)·

Example 1 Catalytic hydrogenation of dienone A typical experimental procedure is as follows:

In a glove box under argon, a solution of Rh(CO)2(acac) and Nixantphos (L2, structure shown in Table) in dichloromethane was stirred for 30 minutes. A dienone solution in ethanol was charged in a 75 mL autoclave, followed by the solution of [Rh(nixantphos)(CO)(acac)] (0.1 or 0.2 mol%) in dichloromethane. The autoclave was closed, purged with hydrogen gas (10 x 20 bar) and pressurized with hydrogen gas at 20 bar or 50 bar depending on the reaction conditions. The autoclave was placed in an oil bath set at 60°C and the reaction was magnetically stirred for the appropriate time. At the end of reaction, the autoclave was cooled down in an ice bath and depressurized. The reaction mixture was concentrated under reduced pressure. Then the crude product was purified by bulb to bulb distillation to yield the desired ketone, otherwise indicated.

Hydrogenation of (E)-5-methyl-6-p-tolylhex-5-en-2-one The autoclave was charged successively with (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2- one (4.081 g, 19.97 mmol) in ethanol (18 mL) and a solution of [Rh(nixantphos)(CO)(acac)] in dichloromethane (2 mL) prepared from Rh(CO)2(acac) (5.0 mg, 0.02 mmol) and Nixantphos (11.6 mg, 0.02 mmol). The reaction mixture was heated for 2 h 30 min under ¾ pressure (20 bar). Purification by bulb to bulb distillation (bp = 157°C under 1.2 mbar) yielded (E)-5-methyl-6-p-tolylhex-5-en-2-one (3.858 g, 18.69 mmol, 94% yield) as a light yellow oil (GC purity = 98%).

¾-NMR (400 MHz, CDChs): 5=1.84 (d, J = 1.3 Hz, 3H), 2.17 (s, 3H), 2.32 (s, 3H), 2.41- 2.44 (m, 2H), 2.62-2.65 (m, 2H), 6.23 (s, 1H), 7.11 ppm (s, 4H).

¹³ C-NMR (100 MHz, CDCI3): 5=208.4 (C), 136.6 (C), 135.7 (C), 135.2 (C), 128.8 (CH), 128.7 (CH), 125.3 (CH), 42.3 (CH2), 34.5 (CH2), 30.0 (CH3), 21.1 (CH3), 17.8 ppm (CH3).

Example 2 Catalytic hydrogenation of dienone of (3E.5E)-5-methyl-6-p-tolylhexa-3.5-dien-2-one

(SI) with various RhX(Ln) complexes

General procedure for the screening of various rhodium complexes with diphosphine Ln : In a glove box, glass vials equipped with a magnetic stirring bar were charged separately with diphosphine (Ln, structure shown in Table 1) (1 mol%) and a solution (1 mL) of the rhodium pre-catalyst (1 mol%) in toluene. After stirring at RT for 1 h, a solution (1 mL, 0.5 M, 0.5 mmol) of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI, structure shown in Table 7) (0.5 mmol/vial) in toluene was added. The vials were placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 5 bar. The reaction was stirred at room temperature for 20 hours. Then, the autoclave was vented and a sample was taken from each vials and analyzed by GC. The results are shown in Table 2.

Table 1 : List of diphosphines used for the hydrogenation.

Table 2: Hydrogenation of SI with various rhodium complexes and LI under hydrogen

(5 bar).

Entry 1 and 2 are comparative examples Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time. Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [((E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[((E)-5-methyl-6-(p-tolyl)hex-5-en-2- one) + sum of other products].

* Potassium acetate was added (10 mol%) to the reaction mixture.

** Dichloromethane was used here instead of toluene. *** Reaction stopped after 4 hours.

Example 3 Catalytic hydrogenation of dienone of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI) with various Rh(COD)CKLn) complexes - Comparative example (conditions reported in W02012150053)

General procedure for the screening of various diphosphines (Ln) with [Rh(COD)Cl] ₂ : In a glove box, glass vials equipped with a magnetic stirring bar were charged separately with the appropriate diphosphines (Ln) as shown in Table 1 (1 mol%), [Rh(COD)Cl]2 (0.5 mol%), potassium acetate (10 mol%) and toluene (1 mL). After stirring at RT for 1 h, a solution (1 mL, 0.5 M, 0.5 mmol) of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI, structure shown in Table 7) in toluene was added. The vials were placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 5 bar. The reaction was stirred at room temperature for 20 hours. Then, the autoclave was vented and a sample was taken from each vials and analyzed by GC. The results are shown in Table 3. Table 3: Hydrogenation of SI with various diphosphine (Ln) and [Rh(COD)Cl]2/AcOK under hydrogen (5 bar).

Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [((E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[((E)-5-methyl-6-(p-tolyl)hex-5-en-2- one) + sum of other products]. Example 4

Catalytic hydrogenation of dienone of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI) with various Rh complexes General procedure for the screening of rhodium complexes with various diphosphines

L1-L4:

In a glove box, glass vials equipped with a magnetic stirring bar were charged separately with the appropriate diphosphines (L1-L4) as shown in Table 1 (1 mol%) and a solution (1 mL) of Rh(CO)2(acac) (1 mol%) in toluene. After stirring at RT for 1 h, a solution (1 mL) of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI as shown in Table 7) (0.5 M, 0.5 mmol) in toluene was added. The vials were placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 5 bar. The reaction was stirred at room temperature for 20 hours. Then, the autoclave was vented and a sample was taken from each vials and analyzed by GC. The results are shown in Table 4.

Table 4: Hydrogenation of SI with Rh(CO)2(acac) and various diphosphines (L1-L4) under hydrogen (5 bar). Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time. Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [((E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[( (E)-5-methyl-6-(p-tolyl)hex-5-en-2-one) + sum of other products]. Example 5

Catalytic hydrogenation of dienone of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI) with various Rh(Ll-L2 complexes in various solvent

General procedure for the screening of Rh(Ll-L2)(CO)(acac) in various solvent:

In a glove box, a glass vial equipped with a magnetic stirring bar was charged with the appropriate preformed Rh(Ll-L2)(CO)(acac) complex (0.5 mol%), followed by (3E,5E)- 5-methyl-6-p-tolylhexa-3,5-dien-2-one (lmmol, SI as shown in Table 7) and the appropriate solvent (2 ml). The vial was placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 5 bar. The reaction was then stirred at 60°C for 4 hours. Then, the autoclave was cooled in an ice/water bath and vented. A sample was taken from the vial and analyzed by GC. The results are shown in Table 5.

Table 5: Hydrogenation of SI with Rh(Ll-L2)(CO)(acac) in various solvent.

Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [((E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[( (E)-5-methyl-6-(p-tolyl)hex-5-en-2-one) + sum of other products].

Example 6

Catalytic hydrogenation of dienone of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI) with Rh complex at various pressure and temperature

General procedure for the screening of Rh(L2)( CO )(acac) at various pressure and temperature:

In a glove box, a stainless steel autoclave equipped with a magnetic stirring bar was charged with the preformed Rh(L2)(CO)(acac) complex (0.1 mol%), followed by (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (5 mmol, SI as shown in Table 7) and EtOH (10 ml). The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at the indicated pressure and the reaction was stirred at the desired temperature for the indicated period of time. Then, the autoclave was cooled in an ice/water bath and vented. A sample was taken from the vial and analyzed by GC. The results are shown in Table 6.

Table 6: Hydrogenation of SI with Rh(L2)(CO)(acac) in EtOH at various ¾ pressure and temperature. Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [(E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[( (E)-5-methyl-6-(p-tolyl)hex-5-en-2-one e) + sum of other products].

Example 7

Catalytic hydrogenation of various dienones (S1-S15) with Rh(L2)(CO)(acac) complex: General procedure for the hydrogenation of dienones with Rh(L2 )( CO)(acac):

In a glove box, a stainless steel autoclave equipped with a magnetic stirring bar was charged with the preformed Rh(L2)(CO)(acac) complex (0.1 mol%) in CH2CI2 (2 ml), followed by the appropriate dienone as shown in Table 7 (20 mmoles) and EtOH (18 ml). The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 20 bar and the reaction was stirred at 60°C for the indicated period of time. Then, the autoclave was cooled in an ice/water bath and vented. The product was isolated by evaporation of the solvent under reduced pressure and purification by column chromatography on silica gel. The results are shown in Table 8. Table 7: List of dienones hydrogenated.

Table 8: Hydrogenation of dienones with Rh(L2)(CO)(acac) in EtOH at 60°C under ¾ pressure (20 bar).

Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of Sl-17 into the desired gamma-delta- unsaturated ketone and into any other products, including the fully saturated aromatic ketones after the indicated time.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [desired gamma-delta- unsaturated ketone]/[desired gamma-delta-unsaturated ketone + sum of other products]. Yield = Isolated yield after purification.

ND = Not determined. * Reaction performed under 50 bar of hydrogen pressure.

** Hydrogenation of both C=C bonds at the 3,4- and 9,10-positions was observed (15%) along with the desired product (71%) and some unidentified isomers of the fully hydrogenated product (7%). Example 8

Catalytic hydrogenation of (2E,4E)-4-methyl-5-(p-tolyl)penta-2,4-dienal with various RhX complexes:

General procedure for the screening of various rhodium complexes with diphosphine LI: In a glove box, glass vials equipped with a magnetic stirring bar were charged separately with Xantphos (LI, structure shown in Table 1) (1 mol%), the rhodium pre-catalyst (1 mol%) and CH2CI2 (1 ml). After stirring at RT for 1 h, a solution (1 mL, 1 M, 1 mmol) of (2E,4E)-4-methyl-5-(p-tolyl)penta-2,4-dienal (S18) (structure shown in Table 7) in CH2CI2 was added. The vials were placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 50 bar. The reaction was stirred at room temperature for 1 hour. Then, the autoclave was vented and a sample was taken from each vials and analyzed by GC. The results are shown in Table 9.

Table 9: Hydrogenation of S18 with various rhodium complexes and LI under hydrogen pressure (50 bar).

Entry 1 to 4 are comparative examples

Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of S18 into the desired aldehyde (E)-4- methyl-5-(p-tolyl)pent-4-enal and any other products, including the saturated alcohol (E)- 4-methyl-5-(p-tolyl)pent-4-en-l-ol after 1 hour in this example.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [(E)-4-methyl-5-(p- tolyl)pent-4-enal]/[(E)-4-methyl-5-(p-tolyl)pent-4-enal + (E)-4-methyl-5-(p-tolyl)pent-4- en-l-ol].

Example 9

Catalytic hydrogenation of (2E,4E)-4-methyl-5-(p-tolyl)penta-2,4-dienal (S18) with various Rh(CO)(acac)(Ln) complexes:

General procedure for the screening of various diphosphines Lit: In a glove box, glass vials equipped with a magnetic stirring bar were charged separately with the appropriate diphosphines (Ln) (1 mol%, as shown in Table 1), Rh(CO)2(acac) (1 mol%), and CH2CI2 (1 mL). After stirring at RT for 1 h, a solution (1 mL, 0.5 M, 0.5 mmol) of (2E,4E)-4-methyl-5-(p-tolyl)penta-2,4-dienal (S18) (structure shown in Table 7) in CH2CI2 was added. The vials were placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 50 bar. The reaction was stirred at room temperature for 1 hour. Then, the autoclave was vented and a sample was taken from each vials and analyzed by GC. The results are shown in Table 10.

Table 10: Hydrogenation ofS18 with various diphosphine (Ln) and Rh(CO)2(acac) under hydrogen (50 bar).

Com/Base = molar ratio in ppm relative to the substrate.

Conv. = conversion (in (%), analyzed by GC) of S18 into the desired aldehyde (E)-4- methyl-5-(p-tolyl)pent-4-enal and any other products, including the saturated alcohol (E)- 4-methyl-5-(p-tolyl)pent-4-en-l-ol after 1 hour in this example.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [(E)-4-methyl-5-(p- tolyl)pent-4-enal]/[(E)-4-methyl-5-(p-tolyl)pent-4-enal + (E)-4-methyl-5-(p-tolyl)pent-4- en-l-ol].

Example 10 Catalytic hydrogenation of (2E,4E)-4-methyl-5-(p-tolyl)penta-2,4-dienal (S18) with Rh(CO)(acac)(Ll) complexes in various solvents:

General procedure for the screening ofRh(Ll )(CO)(acac) in various solvent:

In a glove box, a glass vial equipped with a magnetic stirring bar was charged with the preformed Rh(Ll)(CO)(acac) complex (0.1 mol%), followed by (2E,4E)-4-methyl-5-(p- tolyl)penta-2,4-dienal (S18) (5mmol, as shown in Table 7) and the appropriate solvent (5 ml). The vial was placed in a 75 mL autoclave. The autoclave was closed, purged with hydrogen gas at 20 bar, and finally pressurized with hydrogen gas at 50 bar. The reaction was then stirred at RT for 1 hour. Then, the autoclave was vented. A sample was taken from the vial and analyzed by GC. The results are shown in Table 11.

Table 11: Hydrogenation of S18 with Rh(Ll)(CO)(acac) in various solvent.

Com/Base = molar ratio in ppm relative to the substrate. Conv. = conversion (in (%), analyzed by GC) of S18 into the desired aldehyde (E)-4- methyl-5-(p-tolyl)pent-4-enal and any other products, including the saturated alcohol (E)- 4-methyl-5-(p-tolyl)pent-4-en-l-ol after 1 hour in this example.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [(E)-4-methyl-5-(p- tolyl)pent-4-enal]/[(E)-4-methyl-5-(p-tolyl)pent-4-enal + (E)-4-methyl-5-(p-tolyl)pent-4- en-l-ol].

Example 11 Catalytic hydrogenation of (3E,5E)-5-methyl-6-p-tolylhexa-3,5-dien-2-one (SI) with Rh(COD)(acac) or Rh(CQh(acac) complexes - Comparative example:

Following the general procedure reported in example 1 and using L2. The results are shown in Table 12.

Table 12: Hydrogenation of SI with Rh(COD)(acac) or Rh(CO)2(acac).

Entry 2 and 3 are comparative examples

Conv. = conversion (in (%), analyzed by GC) of SI into the desired product (E)-5- methyl-6-(p-tolyl)hex-5-en-2-one and to any other products, including fully saturated aromatic ketone 5-methyl-6-(p-tolyl)hexan-2-one and deconjugated enone 5-methyl-6-(p- tolyl)hex-4-en-2-one (mixture of E and Z isomers) after the indicated time.

Sel. = selectivity (in (%), analyzed by GC) and calculated as 100 x [((E)-5-methyl-6-(p- tolyl)hex-5-en-2-one)]/[( (E)-5-methyl-6-(p-tolyl)hex-5-en-2-one) + sum of other products].