Process for preparing enantiomerically enriched 2-alkoxy-3-phenylpropionic acids
The present invention relates to a process for preparing enantiomerically enriched, optionally substituted 2-alkoxy-3-phenylpropionic acids by asymmetrically hydrogenating alkoxycinnamic acids.
1. Process for preparing enantiomerically enriched compounds of the general formula (I)
where
R 1 is an optionally substituted C 1 -C 18 -alkyl radical, an optionally substituted C 4 -C 24 -aryl radical or an optionally substituted C 5 -C 18 -arylalkyl radical,
R 2 are each independently OH, halogen, pseudohalogen, amino, an optionally substituted C 1 -C 18 -alkyl radical, an optionally substituted C 1 -C 18 -alkoxy radical, an optionally substituted C 4 -C 24 -aryl radical, an optionally substituted C 5 -C 18 -arylalkyl radical, an optionally substituted C 1 -C 18 -alkylsulphonyl radical, an optionally substituted C 1 -C 18 -alkylcarboxyl radical, an optionally substituted C 1 -C 18 -alkylcarbonyl radical, an optionally substituted C 1 -C 18 -mono- or dialkylamino radical, an optionally substituted C 1 -C 18 -alkylsulphonylamino radical or an optionally substituted C 1 -C 18 -acylamino radical, and
n is 0 or an integer from 1 to 5, characterized in that compounds of the general formula (II)
where
R 1 , R 2 and n are each as defined for the general formula (I) are hydrogenated enantioselectively in a solvent and in the presence of a transition metal hydrogenation catalyst system comprising at least one transition metal compound and at least one ligand, wherein the transition metal compound(s) and ligand(s) are soluble in the solvent, and wherein the ligand is selected from the group consisting of (−)-2,2′-dichloro-3,3′-dimethoxy-6,6′-bis(diphenylphosphinyl)biphenyl, (−)-3,3′-bis(diphenylphosphinyl)-[4,4′]bi(dibenzofuranyl), and the particular enantiomer.
2. Process according to claim 1 , wherein the compounds of the general formula (II) are prepared from compounds of the general formula (III)
where
R 2 and n are each as defined in claim 1 , and compounds of the general formula (IV)
where
R 3 is H or an optionally substituted C 1 -C 18 -alkyl radical, preferably a C 1 -C 6 -alkyl radical, and R 1 is as defined in claim 1 in an aldol reaction in the presence of a base, and subsequent hydrolysis if appropriate.
3. Process according to claim 1 , wherein R 1 is an optionally substituted C 1 -C 6 -alkyl radical, preferably methyl.
4. Process according to claim 1 , wherein R 2 is independently OH, F, Cl, Br, CN, an optionally substituted C 1 -C 6 -alkyl radical, an optionally substituted C 6 -C 24 -aryl radical or an optionally substituted C 5 -C 18 -arylalkyl radical, preferably OH.
5. Process according to claim 1 , wherein n is 1, 2 or 3, preferably 1.
6. Process according to claim 1 , wherein the transition metal hydrogenation catalyst system comprises at least one ruthenium, rhodium, or iridium compound and at least one ligand.
7. Process according to claim 1 , wherein the transition metal hydrogenation catalyst systems comprises ruthenium, rhodium or iridium compounds of the Ru(II), Rh(I), Ir(I) oxidation states, in each case in combination with a chiral diphosphine ligand.
8. Process according to claim 1 , wherein the ruthenium, rhodium or iridium compound used is [RuCl 2 (p-cymene)] 2 , Ru(COD)Cl 2 , [Ru(C 6 H 6 )Cl 2 ] 2 , Rh(COD) 2 BF 4 , [Rh(COD)Cl] 2 , Rh(NBD) 2 BF 4 , [Rh(NBD)Cl] 2 , Ir(COD) 2 BF 4 or [Ir(COD)Cl] 2 .
9. Process according to claim 1 , wherein the enantioselective hydrogenation is performed in the presence of at least one protic solvent.
10. Process according to claim 9 , wherein the solvents used are selected from the group consisting of alcohols, carboxylic esters, halogenated aliphatic hydrocarbons, cyclic or aliphatic ethers, cyclic or aliphatic hydrocarbons, aromatic hydrocarbons, or or mixtures thereof or comprising one or more thereof.
11. Process according to claim 1 , wherein the enantioselective hydrogenation is performed at temperatures of 10° C. to 120° C.
12. Process according to claim 1 , wherein the enantioselective hydrogenation is performed at 1 to 200 bar of hydrogen pressure.
13. Process according to claim 2 , wherein the base used in the aldol reaction comprises alkali metal or alkaline earth metal C 1 -C 18 -alkoxides or optionally substituted alkali metal or alkaline earth metal C 1 -C 18 -amides.
14. Process according to claim 2 , wherein the aldol reaction is performed in the presence of at least one solvent.
15. Process according to claim 14 , wherein the solvents used are selected from the group consisting of alcohols, cyclic or open-chain ethers, aromatic hydrocarbons, cyclic or aliphatic hydrocarbons, or mixtures thereof or comprising one or more thereof.
16. Process according to claim 2 , wherein the aldol reaction is performed at temperatures of 10° C. to 120° C.
17. Process according to claim 1 , wherein the compounds of the general formula (I) are crystallized out without intermediate isolation in the presence of an alkali metal or ammonium salt directly as salts of the general formula (V)
where
M + is an alkali metal cation or ammonium, preferably Na + , and
R 1 , R 2 and n are each as defined in claim 1 .
18. Process according to claim 1 , wherein the at least one transition metal compound is at least one iridium compound.