Process for preparation of propionic acid derivatives

(R)(+)-2-[4-(5-chloro 3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid propinyl ester is produced by converting a compound of formula II ##STR1## in an inert organic solvent, without isolation of the intermediate products, with M.sub.2 CO.sub.3, in which M is sodium or potassium, into the compound of formula III ##STR2## reacting this with the compound of formula IV ##STR3## to form the compound of formula V ##STR4## and converting this with a compound of formula VI ##STR5## wherein Z signifies phenylsulphonyl, tosyl, methylsulphonyl, nosyl, bromophenyl, Cl-, Br- or CICO-, into the compound of formula I.

The present invention relates to a process for the preparation of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester.
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester possesses herbicidal activity and is described for example
 in EP-A-0 248 968.
 [4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid derivatives
 may be produced for example in accordance with EP-A-0 439 857, by reacting
 5-chloro-2,3-difluoropyridine with corresponding 4-hydroxypropionic acid
 esters in the presence of a water-free base and in the absence of a
 solvent. However, this process is unsuitable for producing
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester, since the triple bonding of the hydroxypropionic acid
 ester is inclined to form polymers under the conditions of the process and
 under basic conditions. In addition, this process is especially
 problematic as regards the safety aspect, since the reaction mixture can
 only be heated without solvents at some risk, owing to the high thermal
 potential of this triple bond.
 According to EP-A-0 248 968, pages 12 to 14,
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester is obtained whereby
 a) in a first step, a compound of formula A
 ##STR6##
 in dimethyl sulphoxide is reacted with a mixture of hydroquinone and
 potassium hydroxide in dimethyl sulphoxide to form a compound of formula B
 ##STR7##
 this compound
 b) in a second step, in dimethyl sulphoxide, is reacted in the presence of
 potassium carbonate with S(-)-lactic acid methyl ester tosylate to form
 the compound of formula C
 ##STR8##
 this compound
 c) in a third step, in dioxane, is reacted in the presence of sodium
 hydroxide solution to form the compound of formula D
 ##STR9##
 this compound
 d) in a fourth step, in toluene, is reacted with thionyl chloride to form
 the compound of formula (E)
 ##STR10##
 which finally, without further isolation, this compound
 e) is reacted with a mixture of triethylamine and propinol in toluene to
 form (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic
 acid propinyl ester.
 This process has the major disadvantage that, because of the four-stage
 reaction procedure, complicated separation and purification steps are
 necessary. This leads to substantial losses of yield. In addition, while
 the process is being carried out, the solvent has to be changed twice.
 This necessitates additional time-consuming and expensive distillation
 steps. The known process is therefore not the optimum one especially for
 application on a large scale.
 The aim of the present invention is therefore to provide a process which
 enables (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic
 acid propinyl ester to be produced in a more simple manner, in higher
 purity and in higher yields.
 It has now been found that
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester of formula I
 ##STR11##
 can be produced in a particularly advantageous manner by converting a
 compound of formula II
 ##STR12##
 in an inert organic solvent, without isolation of the intermediate
 products, with M.sub.2 CO.sub.3, in which M is sodium or potassium, into
 the compound of formula III
 ##STR13##
 wherein M is sodium or potassium, reacting this compound with the compound
 of formula IV
 ##STR14##
 to form the compound of formula V
 ##STR15##
 wherein M is sodium or potassium, and converting this compound with a
 compound of formula VI
 ##STR16##
 wherein Z signifies a leaving group such as phenylsulphonyl, tosyl,
 methylsulphonyl, nosyl, bromophenyl, Cl-, Br- or CICO-, into the compound
 of formula I.
 The starting compounds may be used in stoichiometric quantities. It is
 preferable to use the compound of formula IV in an excess of 0.05 to 0.3
 equivalents, most preferably 0.1 equivalents, based on the compound of
 formula III. The compound of formula VI is preferably employed in an
 excess of 0.05 to 0.15 equivalents.
 Within the scope of the present invention, M in M.sub.2 CO.sub.3 is
 preferably potassium.
 Suitable inert organic solvents within the scope of the present invention
 are in particular ketones, esters and ethers. Dimethyl formamide, dimethyl
 sulphoxide, N-methyl pyrrolidone or acetonitrile are especially suitable
 as solvents. Dimethyl formamide and acetonitrile are preferred in
 particular, most preferably dimethyl formamide. In a preferred embodiment
 of the process according to the invention, in formula VI, Z is chlorine.
 The process according to the invention can be carried out at elevated
 temperatures, especially at 40 to 120.degree. C. A temperature range of
 60.degree. to 90 .degree. C., most preferably 70 to 75.degree. C., is
 preferred.
 The reaction of formula II with formula IV may be carried out in the
 presence of a phase transfer catalyst in order to speed up the reaction.
 Suitable phase transfer catalysts are for example quatemary ammonium
 salts, quatemary phosphonium salts or crown ethers.
 The starting compounds of formulae II, IV and VI are known or may be
 produced by known processes. The compound of formula IV is described for
 example in EP-A-0 248 968, and the compound of formula II in EP-A-0 083
 556. Compounds of formula VI, wherein Z is chlorine, may be produced for
 example according to J. Am. Chem. Soc. 77, 1831(1955), whereby suitable
 bases for this reaction are pyridine and preferably
 5-ethyl-2-methylpyridine.
 The process according to the invention is distinguished from known
 processes in particular by the fact that it can be carried out as a
 one-pot process without changing the solvent. In this way, not only is the
 expenditure on apparatus considerably lower, but by avoiding complex
 separation and distillation steps, there is also a substantial saving in
 time. In addition, the substantial reduction in solvent residues achieved
 with the process according to the invention is particularly advantageous
 from an ecological point of view. The lower thermal loading of the product
 reduces the formation of undesired by-products and the particularly
 selective course of the reaction enables a more precise dosaging of the
 reactants to be achieved, which in turn leads to a higher yield and a
 product with considerably improved purity.

PREATIVE EXAMPLES
 Example P1
 Preparation of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester
 182 g of (R)-2-(p-hydroxyphenoxy)-propionic acid 100% (1 mol) in 600 g of
 DMF are converted into the corresponding potassium salt by adding 69 g of
 potassium carbonate powder (0.5 mols) at 70.degree. C. whilst cleaving the
 CO.sub.2. To this solution are added 193 g of potassium carbonate powder
 (1.4 mols) and then, at a temperature of 70-75.degree. C., 165 g of
 5-chloro-2,3-difluoropyridine (1.1 mols) are added over the course of 30
 minutes. After 4 hours, the compound of formula V thus obtained is reacted
 totally, by measuring in 86 g of propargyl chloride (1.15 mols) as a
 60-70% toluene solution over the course of 2 hours directly, without
 isolation, at a temperature of 70-75.degree. C., to form the
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester. The salts are filtered off, washed with 300 g of DMF in
 portions, and the filtrate is concentrated to the melt on a rotary
 evaporator under vacuum at a temperature of 120.degree.C. The crude melt
 of the (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic
 acid propinyl ester is mixed at a temperature of 50.degree.C. with 300 g
 of ethanol/water 9:1, seeded at a temperature of 30 to 35.degree. C. and
 cooled to a temperature of 0 to 50.degree. C. The crystal pulp is added to
 a suction filter, washed with 70 g of ethanol/water 9:1, and dried under
 vacuum at a temperature of 30 .degree.C. 307 g of active substance are
 obtained with a content of 97 % (GC), corresponding to a yield of 85% of
 theory, based on (R)-2-(p-hydroxyphenoxy)-propionic acid.
 Example P2
 Preparation of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester
 182 g of (R)-2-(p-hydroxyphenoxy)-propionic acid 100% (1 mol) in 1500 g of
 acetonitrile are converted into the corresponding potassium salt by adding
 69 g of potassium carbonate powder (0.5 mols) at 70.degree.C. whilst
 cleaving the CO.sub.2. Then, 193 g of potassium carbonate powder (1.4
 mols) and 2 g of tetrabutyl ammonium bromide as the phase transfer
 catalyst are added to the reaction mixture, and at a temperature of 70 to
 75.degree. C., 165 g of 5-chloro-2,3-difluoropyridine (1.1 mols) are added
 over the course of 30 minutes. After 8 hours, the compound of formula V
 thus obtained is reacted totally, by measuring in 154 g of propargyl
 mesylate (1.15 mols) as a 60-70% toluene solution over the course of 2
 hours, directly, without isolation, at a temperature of 70-75.degree. C.,
 to form the
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester. Working up is effected analogously to example P1. 304 g of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester are obtained with a content of 98% (GC), corresponding to a
 yield of 85% of theory, based on (R)-2-(p-hydroxyphenoxy)-propionic acid.
 Example P3
 Preparation of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester
 If the propargyl chloride of example P1 is replaced by 226 g (1.15 mols) of
 benzosulpho acid propargyl ester, 305 g of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester are obtained with a content of 96%% (GC), corresponding to
 a yield of 84%% of theory, based on (R)-2-(p-hydroxyphenoxy)-propionic
 acid.
 Example P4
 Preparation of
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester
 182 g of (R)-2-(p-hydroxyphenoxy)-propionic acid 100% (1 mol) in 1500 g of
 acetonitrile are converted into the corresponding potassium salt by adding
 69 g of potassium carbonate powder (0.5 mols) at 70.degree. C. whilst
 cleaving the CO.sub.2. Then, 193 g of potassium carbonate powder (1.4
 mols) and 2 g of tetrabutyl ammonium bromide as the phase transfer
 catalyst are added to the reaction mixture, and at a temperature of 70 to
 75.degree. C., 165 g of 5-chloro-2,3-difluoropyridine (1.1 mols) are added
 over the course of 30 minutes. After 8 hours, the compound of formula V
 thus obtained is reacted totally to form the
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester, directly, without isolation, at a temperature of
 70-75.degree. C., by measuring in chloroformic acid propargyl ester,
 whereby CO.sub.2 is released. Working up is effected analogously to
 example P1.
 (R)(+)-2-[4-(5-chloro-3-fluoropyridin-2-yloxy)-phenoxy]-propionic acid
 propinyl ester is obtained with a content of 97% (GC), corresponding to a
 yield of 80% of theory, based on (R)-2-(p-hydroxyphenoxy)-propionic acid.