The present invention relates to a process for the preparation of a (p-chlorophenyl)propanol derivative which can be a useful intermediate for an antiplatelet.
The compound represented by the formula (3) is a compound useful as an antiplatelet, as disclosed in JP-B- 7-107055, EP 482208A and U.S. Pat. No. 5,314,883. 
The process for the preparation of the compound (3) as disclosed in the above patents, comprises condensing a compound (2) with a compound (4), and further reacting 3-picolylamine thereto, followed by conversion to a hydrochloride, as shown in Scheme 1. 
In order to obtain this bromine compound (2) initially, the production was carried out by a process via a p-chlorocinnamate derivative, as shown in Scheme 2, but it was difficult to suppress a dechlorination reaction during the hydrogenation of the double bond. 
Then, we paid attention to a reaction for synthesizing a compound (7) by subjecting p-iodochlorobenzene and allyl alcohol to Pd coupling at a relatively low temperature in the presence of a quaternary ammonium salt having a relatively large alkyl group such as tetrabutylammonium chloride, as reported in J.C.S. in 1984 (J. Chem. Soc. Commun., 1984, 19, 1287-1289), because if this compound is reduced, the required alcohol compound can easily be obtained. However, according to the reaction conditions disclosed in this literature, the amount of palladium acetate to be used is relatively large at a level of from 1 to 2 mol %, and the quaternary ammonium salt is expensive and has a large molecular weight. Therefore, this process was considered to be not proper as an industrial process (in the same literature, a study was made on the types of quaternary ammonium salts, and as a result, tetrabutylammonium chloride was selected). Further, inclusion of a branched isomer (compound (8)) and its reduced form (9) formed in an amount of a few %, was also a problem which must have been solved. 
In the course of a strenuous study, we have found that if the quaternary ammonium salt is changed to tetramethylammmonium chloride without changing other conditions disclosed in the literature, although the reaction rate is very slow (reaction temperature: room temperature), when the reaction temperature is raised to at least 50xc2x0 C., the desired reaction will proceed very efficiently. As a result, the amount of palladium acetate to be used may be sufficient even at a level of 0.1 mol %. By this reaction, the above-mentioned branched isomer will be formed in an amount of about 6%, but it has been found that if bromination is carried out as it stands, to obtain a compound (2), and the condensation with the compound (4) is carried out, the branched bromine compound will be dehydrobrominated by the base and will not react with the compound (4). Namely, the branched isomer formed by the Pd coupling, requires no special separation operation.
Further, the aldehyde intermediate as the coupling product may be isolated, and its structure has already been identified. However, it has been experimentally confirmed that it may be subjected to the next reaction without isolating it. Namely, simply by adding sodium borohydride to the reaction solution after confirming the progress of coupling, it may be led to the alcohol compound (1).
Namely, the present invention relates to a process for the preparation of an intermediate of a pyridazinone (formula (3)), characterized by subjecting p-iodochlorobenzene to Pd coupling with ally alcohol in the presence of tetramethylammonium chloride, followed by reduction to obtain an alcohol compound (1), which is further brominated to a compound (2). 
Process for the preparation of compound (1) (Pd coupling reaction and reduction)
The solvent to be used for the reaction is preferably of an amide type such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone or dimethylimidazolidinone, and it may be used alone or as mixed with e.g. an aromatic hydrocarbon such as toluene or xylene. It is a feature of the present invention to use tetramethylammonium chloride which is most inexpensive and has a small molecular weight (i.e. the amount to be used, being small), as a quaternary ammonium salt, and the amount to be used, is within a range of from 0.5 to 3 times by mol, preferably from 0.9 to 1.5 times by mol. It is also a feature of the present invention that the amount of palladium acetate as the catalyst may be reduced and is within a range of from 0.01 to 0.2 mol %, preferably within a range of from 0.05 to 0.15 mol %. As the base, sodium hydrogencarbonate or sodium carbonate is required, and the amount to be used is within a range of from an equimolar amount to 20 times by mol, preferably within a range of from 3 to 10 times by mol. The reaction temperature is within a range of from 50 to 150xc2x0 C., preferably within a range of from 50 to 100xc2x0 C.
The aldehyde compound may be extracted with ethyl acetate or toluene after distilling the solvent off, and may be isolated as an intermediate. However, it is preferred to carry out the reduction of the next step as it stands without isolating it. Namely, after confirming the formation of the aldehyde intermediate by gas chromatogram, the reaction solution is cooled to xe2x88x9220 to 10xc2x0 C., and from 0.25 to 1 time by mol, preferably from 0.25 to 0.35 time by mol, of sodium borohydride is added, whereby the reduction of the aldehyde can be carried out within a reaction time of one hour.
Process for the Preparation of Compound (2) (Bromination Reaction)
Using an aromatic hydrocarbon solvent such as toluene or xylene, bromination of the alcohol compound (1) can be carried out with phosphorus tribromide. The amount of phosphorus tribromide to be used, is from 0.3 to 2 times by mol, preferably from 0.5 to 1.2 times by mol, and the reaction temperature is within a range of from 50 to 150xc2x0 C.
The process for the preparation of a (p-chloropheny)propanol derivative according to the present invention is an efficient process, whereby a dechlorination reaction which takes place in the conventional process, is not observed. Further, the amount of palladium acetate used during the coupling, was not more than {fraction (1/10)}.
USPTO Backgrounds
USPTO Backgrounds