3-substituted-alpha,beta-dibromoethylbenzene and process for preparing the same

Abstract: A novel 3-substituted α,β-dibromoethylbenzene of formula (I): wherein X represents a halogen atom or a trihalomethyl group, which is a useful intermediate for pharmaceuticals or agricultural chemicals, is prepared by a simple and high yield process which comprises reacting a 3-substituted α-bromoethylbenzene represented by formula (II): wherein X is as defined above, or a 3-substituted ethylbenzene represented by formula (III): wherein X is as defined above, with bromine in the presence of a quaternary ammonium salt.

Description: This invention relates to a 3-substituted-α,β-dibromoethylbenzene, which is a novel and useful intermediate compound for pharmaceuticals and agricultural chemicals, and also relates to a process for preparing the 3-substituted-α,β -dibromoethylbenzene. Chlorostyrene oxide derivatives are used in the preparation of a useful antidiabetic agent or anti-obese agent (see U.S. Patent 5,061,727). Known processes for preparing the 3-chlorostyrene oxide, which is a key intermediate for the chlorostyrene oxide derivatives, include a process of reducing chloro-α-bromoacetophenone, followed by cyclization (JP-A-4-218384 corresponding to USP 5266485, and JP-A-8-119890, the term "JP-A" as used herein means an "unexamined published Japanese patent application"); a process of epoxidizing chlorostyrene (Yuki Gosei Kagaku, Vol. 43, p. 162 (1987); and a process of starting with chlorobenzaldehyde (JP-A-51 105024). However, these processes have several disadvantages for industrial application: (1) chloro-α-bromoacetophenone, which is obtained by bromination of chloroacetophenone, is lacrimatory and difficult to handle; (2) industrially available styrenes are limited; (3) reaction reagents used, such as LiAlH 4 , are expensive; and (4) the yield is low. Therefore, development of a new route for synthesizing 3-chlorostyrene oxide has been desirable. On the other hand, a substituted-α,β-dibromoethylbenzene is considered useful as a starting material, since this compound can be hydrolyzed to a corresponding bromohydrin compound, which is then cyclized to give a substituted stvrene oxide derivative. Mesnard et al mention the methods of preparing derivatives of types Ar-C≡CH and Ar-C≡CR in J. Chem. Res., Synop., 81 (9), 270-1, 1981, and one of these methods utilizes dibromoethylbenzene, whose phenyl group contains a substituent F or CF 3 , as a starting material. However, this article as such does not give further details about how to prepare dibromoethylbenzene and its substituent. Nevertheless, only one process is known for preparing α,β-dibromoethylbenzene, in which bromine is added to a styrene compound ( Annalen , 154, 154 (1870)). However, this process is not practical because industrially available styrene compounds are limited. Therefore, there has been a demand for developing a novel and industrially advantageous process for preparing α,β-dibromoethylbenzene. As a result of extensive studies, the inventors have found that a novel 3-substituted-α,β-dibromoethylbenzene which is a useful intermediate for pharmaceuticals and agricultural chemicals can be obtained by reacting a 3-substituted-α-bromoethylbenzene or a 3-substituted ethylbenzene with bromine in the presence of a quaternary ammonium salt. The present invention was thus made based on this finding. The present invention provides a 3-substituted α,β-dibromoethylbenzene represented by formula (I): wherein X represents a halogen atom or a trihalomethyl group. The present invention also provides a process for preparing the 3-substituted α,β-dibromoethylbenzene represented by formula (I): wherein X represents a halogen atom or a trihalomethyl group, which comprises reacting a 3-substituted α-bromoethylbenzene represented by formula (II): wherein X represents a halogen atom or a trihalomethyl group, or a 3-substituted ethylbenzene represented by formula (III): wherein X represents a halogen atom or a trihalomethyl group, with bromine in the presence of a quaternary ammonium salt. The present invention will be described in detail below. The 3-substituted-α,β-dibromoethylbenzene (I) according to the present invention is a novel compound which was synthesized by the inventors for the first time. The substituent X on the benzene ring is a halogen atom or a trihalomethyl group. The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and the trihalomethyl group includes a trifluoromethyl group, a trichloromethyl group, and a tribromomethyl group. Of the compounds (I), those having a halogen atom, particularly a chlorine atom, as X are a useful intermediate not only for the above-described pharmaceuticals but also for agricultural chemicals (see JP-A-2-304043). Use of this compound (I) provides new routes for the production of the above-described pharmaceuticals and agricultural chemicals, these routes being simpler and more economical than conventional techniques. For example, in the preparation of the 3-chlorophenylethanolamine derivative described in U.S. Patent 5,061,727, 3-chloro-α,β-dibromoethylbenzene is converted to a bromohydrin, which is then cyclized to give 3-chlorostyrene oxide, as shown in the following reaction scheme. An optically active styrene oxide can be obtained by optical resolution either before or after the cyclization. Thereafter, the resulting styrene oxide is reacted with a necessary amine compound to obtain a desired compound. etc. For the preparation of the herbicides having an indanedione skeleton described in JP-A-2-304043, hydrogen bromide is eliminated from 3-chloro-α,β-dibromoethylbenzene to prepare 3-chloro-α-bromostyrene, as shown in the following reaction scheme. Then, the resulting bromostyrene derivative is converted to an allyl alcohol derivative or an allyl chloride derivative, which is then reacted with an indanedione derivative, followed by epoxidation, to give a desired compound. The α,β-dibromoethylbenzene derivative of formula (I) according to the present invention can be prepared by reacting an α-bromoethylbenzene derivative represented by formula (II) or an ethylbenzene derivative represented by formula (III) with bromine in the presence of a quaternary ammonium base. The substituent X in the above formulae (II) and (III) is a halogen atom or a trihalomethyl group. The halogen atom includes a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and the trihalomethyl group includes a trifluoromethyl group, a trichloromethyl group, and a tribromomethyl group. The bromination reaction of a substituted benzene nucleus proceeds in the same manner as in bromination of an unsubstituted benzene nucleus irrespective of the position or kind of the substituent on the benzene ring provided that the substituent is an electron attracting group such as a halogen atom, a trihalomethyl group, a nitro group, a cyano group, a sulfo group, an alkyl ester group, etc. In the reaction to form α,β-dibromoethylbenzene derivative (I) from the α-bromoethylbenzene derivative (II), bromine is used in an amount of 1 to 2 molar equivalents, preferably 1 to 1.5 molar equivalents, to the α-bromoethylbenzene derivative (II) in order to ensure a satisfactory yield. In the reaction to form α,β-dibromoethylbenzene derivative (I) from the ethylbenzene derivative (III), bromine is used in an amount of 2 to 3 molar equivalents, preferably 2 to 2.5 molar equivalents, to the ethylbenzene derivative (III) in order to ensure a satisfactory yield. When starting with the ethylbenzene derivative, a monobrominated compound may first be prepared, which is further brominated to a dibrominated compound. The monobromination reaction may require light or a radical initiator. The light irradiation is carried out usually with light having a wavelength of 200 nm to 800 nm. Commonly employed oil-soluble radical initiators may be used with no particular limitation. Examples of suitable radical initiators include azo compounds such as azobisisobutyronitrile (AIBN) and peroxide compounds such as benzoyl peroxide (BPO). The radical initiator is used in an amount of 0.1 X 10 -6 to 0.1 molar equivalent, preferably 0.1 X 10 -5 to 0.01 molar equivalent, to the ethylbenzene derivative (III). The reaction is carried out by heating at or above the decomposition point of the radical initiator used. The bromination reaction is preferably carried out in the absence of a solvent from the standpoint of production efficiency. If desired, the reaction system may be diluted appropriately with an organic solvent. Examples of the suitable solvents include halogenated hydrocarbons such as carbon tetrachloride and chloroform; hydrocarbons such as benzene, cyclohexane, hexane, and heptane; and ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, and dibutyl ether. While not limiting, the solvent is used in an amount of from 0 to 1000 times, preferably from 0 to 200 times, the volume of the starting compound (i.e., the α-bromoethylbenzene derivative (II) or the ethylbenzene derivative (III)). The quaternary ammonium salts to be used include tetramethylammonium hydroxide, tetraethylammonium hydroxide, trimethylbenzylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium bromide, triethylbenzylammonium bromide, trimethylphenylammonium bromide, triethylbenzylammonium chloride, tetramethylammonium chloride, trioctylmethylammonium chloride, tributylbenzylammonium chloride, trimethylbenzylammonium chloride, N-laurylpyridinium chloride, N-benzylpicolinium chloride, N-lauryl-4-picolinium chloride, N-laurylpicolinium chloride, tricaprylmethylammonium chloride, tetramethylammonium iodide, tetra-n-butylammonium iodide, and tetrabutylammonium hydrogensulfate. Commercially available quaternary ammonium salts may be utilized. Preferred quaternary ammonium salts are those having a hydrogensulfate ion, a chloride ion or a bromide ion as an anion moiety, such as tetramethylammonium bromide, tetraethylammonium bromide, tetrabutylammonium bromide, triethylbenzylammonium bromide, trimethylphenylammonium bromide, triethylbenzylammonium chloride, tetramethylammonium chloride, trioctylmethylammonium chloride, tributylbenzylammonium chloride, trimethylbenzylammonium chloride, N-laurylpyridinium chloride, N-benzylpicolinium chloride, N-lauryl-4-picolinium chloride, N-laurylpicolinium chloride, and tetrabutylammonium hydrogensulfate. More preferred are those having a hydrogensulfate ion or a chloride ion as an ion moiety, such as triethylbenzylammonium chloride, tetramethylammonium chloride, trioctylmethylammonium chloride, tributylbenzylammonium chloride, trimethylbenzylammonium chloride, N-laurylpyridinium chloride, N-benzylpicolinium chloride, N-lauryl-4-picolinium chloride, N-laurylpicolinium chloride, and tetrabutylammonium hydrogensulfate. The amount of the quaternary ammonium salt to be used is important to obtain the compound of the present invention. While it may vary depending on the reaction temperature and the amount of bromine, an excessive amount of the quaternary ammonium salt is not preferable, since bromination on the benzene ring may occur. Generally, the quaternary ammonium salt is used in an amount of 0.5 X 10 -3 to 0.5 molar equivalent, preferably 0.001 to 0.1 molar equivalent, more preferably 0.001 to 0.03 molar equivalent, to the α-bromoethylbenzene derivative (II) or the ethylbenzene derivative (III). When the ethylbenzene derivative (III) is used, the quaternary ammonium salt may be added to the reaction system from the very beginning or afterwards. From the viewpoint of reaction yield, it is recommended to add the quaternary ammonium salt after 1 molar equivalent of bromine per ethylbenzene derivative has been added. The reaction of the α-bromoethylbenzene derivative (II) and bromine is carried out at a temperature of from 20 to 150°C, preferably from 20 to 100°C, more preferably from 50 to 100°C. Bromine is added dropwise, and after completion of the dropwise addition, the reaction is continued for a period of 30 minutes to 3 hours. The reaction of the ethylbenzene derivative (III) and bromine is carried out at a temperature of from 0 to 200°C, preferably from 20 to 150°C, more preferably from 20 to 100°C. Bromine is added dropwise, and after completion of the dropwise addition, the reaction is continued for a period of 30 minutes to 3 hours. A preferred mode of reaction for the ethylbenzene derivative (III) is as follows. One molar equivalent of bromine per ethylbenzene derivative (III), in the whole amount of bromine to be used, is added dropwise at 0 to 200°C, preferably 0 to 150°C. If desired, this process is effected in the presence of light or a radical initiator. After the addition of that amount of bromine, the system is allowed to react for a period of 30 minutes to 3 hours. Preferably, a quaternary ammonium salt is added around at this stage. Subsequently, the rest of bromine is added dropwise at 20 to 150°C, preferably 20 to 100°C, more preferably 50 to 100°C, and after the addition, the system is further allowed to react for a period of 30 minutes to 3 hours, if desired, at an elevated temperature, so as to complete the reaction. The rest of bromine may be added either all at once or in divided portions, and after the addition, the reaction temperature may be raised appropriately during the reaction. After completion of the reaction, the reaction mixture is cooled to room temperature, washed with an aqueous solution of a reducing agent such as sodium thiosulfate, or an aqueous solution of an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate or sodium hydrogencarbonate, to remove any untreated bromine, and extracted with an organic solvent for concentration to isolate the α,β-dibromoethylbenzene derivative (I). If necessary, the product can further be purified by recrystallization, distillation, or the like. The α-bromoethylbenzene derivative (II) can easily be synthesized by known processes described in the literature, e.g., J. Org. Chem., Vol. 232 (1), pp. 59-70 (1982) and Collect. Gzech. Chem. Commun., Vol. 41 (2), pp. 633-646 (1976). The α-bromoethylbenzene derivative (II) can easily be synthesized since it is an intermediate formed in the reaction between the ethylbenzene derivative (III) and bromine, when preparing the dibrominated compound (I). The ethylbenzene derivative (III) can easily be synthesized by isomerizing a commercially available monohalo- or trihalomethyl-substituted ethylbenzene to a 3-substituted compound. It can also be prepared by introducing an ethyl group to benzene substituted with a halogen atom, etc. through Friedel-Crafts reaction or by diazotization of commercially available 3-aminoethylbenzene followed by halogenation. Hydrogen bromide can easily be eliminated from the α,β-dibromoethylbenzene derivative (I) according to the present invention by reacting with a base to give an α-bromostyrene derivative represented by formula (IV): wherein X is a halogen atom or a trihalomethyl group. Examples of the bases to be used include inorganic bases such as sodium hydroxide, potassium hydroxide, potassium carbonate, and calcium carbonate; and organic bases such as triethylamine, diazabicycloundecene (DBU), and pyridine. The amount of the base to be used is not particularly limited provided that it is at least 1 molar equivalent to the α,β-dibromoethylbenzene derivative (I). The reaction is carried out at -20 to +200°C, preferably 0 to 150°C, more preferably still 30 to 120°C, for a period of 10 minutes to 10 hours. While not limiting, the amount of the solvent is from 0 to 1000 times, preferably 0 to 200 times, the volume of the α,β-dibromoethylbenzene derivative (I). The elimination of hydrogen bromide using the base can be carried out in water, an organic solvent, or a two-phase solvent of water and an organic solvent in the presence of a catalyst. It is preferable to add an inorganic base and to carry out the reaction in water or a two-phase solvent of water and an organic solvent in the presence of a catalyst. In this preferred procedure, the treatment after the reaction is easy. Examples of suitable catalysts include quaternary ammonium salts and quaternary phosphonium salts. Since the quaternary ammonium salt that has been used in the preparation of the α,β-dibromoethylbenzene derivative (I) can serve as a catalyst in the elimination of hydrogen bromide, the reaction may be continued without isolating the α,β-dibromoethylbenzene derivative (I), which is industrially advantageous and preferred. When water is used as a solvent, the reaction mixture is extracted with an appropriate organic solvent, followed by concentration thereof to isolate the α-bromostyrene derivative (IV). When a two-phase solvent of water and an organic solvent is used, the reaction mixture is subjected to liquid-liquid separation, and the organic layer is collected and concentrated to isolate the α-bromostyrene derivative (IV). If necessary, the product can further be purified by recrystallization, distillation, or the like. The product obtained above is distilled under reduced pressure. The degree of vacuum is controlled so that the α-bromostyrene derivative (IV) may be distilled off in a temperature range of from -20° to +200°C, preferably from 0 to 150°C, more preferably from 30 to 120°C. The above and other objects, features and advantages will be made apparent from the following description of the preferred embodiments, given as a non-limiting example, with reference to the examples. Unless otherwise indicated, all percentages are indicated by weight. PREPARATION EXAMPLE Synthesis of 3-Chloro-α-bromoethylbenzene from 3-Chloroethylbenzene A catalytic amount of AIBN was added to 2.0 g (14.2 mmol) of 3-chloroethylbenzene. Bromine (3.4 g; 21.3 mmol) was added thereto dropwise at 60°C over a period of 5 minutes under shielding from light. During the addition, hydrogen bromide was vigorously given off. The reaction mixture was stirred at 60°C for 30 minutes. Gas chromatography analysis of the resulting reaction mixture revealed that 3-chloro-α-bromoethylbenzene had been prepared in a yield of 90% or higher. EXAMPLE 1 Synthesis of 3-Chloro-α,β-dibromoethylbenzene from 3-Chloroethylbenzene To 5.0 g (35.6 mmol) of 3-chloroethylbenzene was added dropwise 6.0 g (37.5 mmol) of bromine at room temperature over a period of 1 hour under irradiation with a 60W fluorescent tube. After the addition, the reaction mixture was further allowed to react at room temperature for 1 hour. Then, 300 mg (1.43 mmol) of tetraethylammonium bromide was dissolved in the reaction mixture, the temperature of the mixture was raised to 80°C, and 6.5 g (40.7 mmol) of bromine was again added over a period of 1 hour. After the addition, the reaction was continued at 80°C for an additional period of 1 hour to complete the reaction. The reaction mixture was cooled to room temperature, diluted with diethyl ether, and washed successively with a 10% aqueous solution of sodium hydroxide and a saturated aqueous solution of sodium chloride. The ether layer was dried over anhydrous sodium sulfate and concentrated to give 10.6 g (purity: 90%) of crude crystals of 3-chloro-α,β-dibromoethylbenzene. The crude crystals were purified by recrystallization from acetone-water. Melting point: 39.3-41.4°C 1 H-NMR (δ, CDCl 3 ): 3.96 (1H, t), 4.06 (1H, q), 5.07 (1H, dd), 7.26-7.40 (4H, m) EXAMPLE 2 Synthesis of 3-Chloro-α,β-dibromoethylbenzene from 3-Chloroethylbenzene To 500 g (3.56 mol) of 3-chloroethylbenzene was added dropwise 571 g (3.57 mol) of bromine in the presence of 15 mg (0.0913 mmol) of AIBN at 50 to 60°C over a period of 1 hour under shielding from light. After the addition, the reaction mixture was stirred for 30 minutes. Then, 6.6 g (0.0355 mol) of benzyltrimethylammonium chloride was added to the reaction mixture, and 571 g (3.57 mol) of bromine was again added dropwise at 60 to 70°C over a period of 3 hours. After the addition, the temperature was increased to 90°C, and the reaction mixture was further stirred for an additional 1-hour period. Then, 115 g (0.718 mol) of bromine was added dropwise over a period of 1 hour, followed by stirring for 1 hour. After completion of the reaction, the reaction mixture was cooled to room temperature, washed once with a 5% aqueous solution of sodium hydroxide and twice with water to give 1.1 kg (yield: 93%) of 3-chloro-α,β-dibromoethylbenzene as a crude product. EXAMPLE 3 Synthesis of 3-Chloro-α,β-dibromoethylbenzene from 3-Chloro-α-bromoethylbenzene To 10 g (45.6 mmol) of 3-chloro-α-bromoethylbenzene was added 155 mg (0.456 mmol) of tetrabutylammonium hydrogensulfate. The reaction mixture was heated to 40°C, and 8.72 g (54.7 mmol) of bromine was added dropwise at 40°C, followed by stirring at that temperature for 1.5 hours, then at 50°C for 2 hours, and finally at 70°C for 2 hours. Gas chromatography analysis of the reaction mixture revealed that 3-chloro-α,β-dibromoethylbenzene had been prepared in a yield of 94%. APPLICATION EXAMPLE Synthesis of 3-chloro-α-bromostyrene In 50 ml of ethanol was suspended 20.8 g (69.7 mmol) of 3-chloro-α,β-dibromoethylbenzene. To the suspension was added 100 ml of an ethanol solution containing 5.8 g (103.4 mmol) of potassium hydroxide at room temperature, and the mixture was stirred at room temperature for 1 hour. After completion of the reaction, the reaction mixture was poured into 150 ml of ice-water and extracted with 300 ml of diethyl ether. The extract was dried over anhydrous sodium sulfate and concentrated to give 15.0 g (purity: 99%) of 3-chloro-α-bromostyrene. 1 H-NMR (CDCl 3 , δ): 5.82 (1H, d), 6.14 (1H, d), 7.26-7.33 (2H, m), 7.45-7.49 (1H, m), 7.57-7.58 (1H, m) As has been described above, the present invention makes it possible to prepare novel α,β-dibromoethylbenzene derivatives, useful intermediates for pharmaceuticals and agricultural chemicals, from easily available starting materials in high yield. These intermediates are used in simpler and more economical new routes for preparing the pharmaceuticals and agricultural chemicals, as compared with those using conventional techniques.

Claims: A 3-substituted α,β-dibromoethylbenzene represented by formula (I): wherein X represents a halogen atom other than fluorine or a trihalomethyl other than the trifluoromethyl group. The compound according to claim 1, wherein X is a halogen atom. The compound according to claim 1, wherein X is a chlorine atom. A process for preparing a 3-substituted α,β-dibromoethylbenzene of formula (I): wherein X represents a halogen atom or a trihalomethyl group, which comprises reacting a 3-substituted α-bromoethylbenzene represented by formula (II): wherein X is as defined above, with bromine in the presence of a quaternary ammonium salt. The process according to claim 4, wherein bromine is used in an amount of from 1 to 2 molar equivalents to the 3-substituted-α-bromoethylbenzene. A process for preparing a 3-substituted α,β-dibromoethylbenzene of formula (I): wherein X represents a halogen atom or a trihalomethyl group, which comprises reacting a 3-substituted ethylbenzene represented by formula (III): wherein X is as defined above; with bromine in the presence of a quaternary ammonium salt. The process according to claim 6, wherein bromine is used in an amount of from 2 to 3 molar equivalents to the 3-substituted ethylbenzene. The process according to claim 6 or 7, wherein said quaternary ammonium salt is added after addition of one molar equivalent per 3-substituted ethylbenzene of the whole bromine. The process according to any one of claims 6 to 8, wherein either the reaction mixture is irradiated with light, or a radical initiator is added to the reaction mixture. The process according to claim 9, wherein said radical initiator is added in an amount of from 0.1 x 10 -6 to 0.1 molar equivalent to the 3-substituted ethylbenzene. The process according to any one of claims 4 to 10, wherein said quaternary ammonium salt has a hydrogensulfate ion, a chloride ion or a bromide ion as an anion moiety. The process according to any one of claims 4 to 11, wherein said quaternary ammonium salt is used in an amount of from 0.5 x 10 -3 to 0.5 molar equivalent to the 3-substituted α-bromoethylbenzene or the 3-substituted ethylbenzene. The process according to any one of claims 4 to 12, wherein said reaction is carried out at a temperature of from 20 to 150°C. The process according to any one of claims 4 to 13, wherein the reaction is carried out in the presence of a solvent. Use of 3-substituted α,β-dibromoethylbenzene as defined in claim 1 for the preparation of a corresponding α-bromostyrene derivative. Use of 3-substituted α,β-dibromoethylbenzene as defined in claim 1 for the preparation of chlorostyrene oxide derivatives.

Inventors: HOSOKAWA AKEMI, KATSURADA MANABU, TANAKA KEN, HOSOKAWA, AKEMI, KATSURADA, MANABU, TANAKA, KEN, Hosokawa, Akemi, c/o Mitsubishi Chem. Corp., Katsurada, Manabu, c/o Mitsubishi Chem. Corp., Tanaka, Ken, c/o Mitsubishi Chem. Corp.
Applicants: MITSUBISHI CHEM CORP, MITSUBISHI CHEMICAL CORPORATION
Application year: 1996
Main classification: C07C22
IPC codes: C07C25, C07C22, C07D303, C07C17