JP2006265169A - Method for production of alkylidene succinic acid compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for effectively producing alkylidene succinic acid compound having a benzophenone skeleton, important as a starting material for synthesis of a photochromic compound. <P>SOLUTION: The invention relates to the method for producing alkylidene succinic acid compound having a benzophenone skeleton by reacting a benzophenone compound such as 4-methocybenzophenone, etc., with a diethylsuccinate in the presence of a metal alkoxide, wherein the metal alkoxide is added as a liquid dissolved or suspended in an ether such as tetrahydrofuran or the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an alkylidene succinic acid compound useful as a raw material for a photochromic compound.

  An alkylidene succinic acid compound having a benzophenone skeleton is an important compound as a raw material for synthesizing photochromic compounds such as indenonaphthopyran (see Patent Document 1). As a method for producing such alkylidene succinic acid, as a method utilizing Stobbe reaction, a metal alkoxide is prepared in t-butanol, and a benzophenone compound and a succinic acid diester are added dropwise thereto and heated to reflux temperature. A method of reacting is known (see Non-Patent Documents 1 and 2). In the Stobbe reaction, when an asymmetric benzophenone compound is used as a raw material, the two isomers are in a ratio of approximately 1: 1 due to rotation around the α-position carbon atom of benzophenone. It is known to generate.

US6340765 Organic Synthesis IV, 132 (1963) J. et al. Am. Chem. Soc. , 72, 511-513 (1979)

  However, the Stobbe reaction has the following problems. That is, first, since t-butanol having a low melting point is used as a reaction solvent in the reaction, t-butanol evaporated at the time of the reaction solvent distilling process after the completion of the reaction adheres to the wall of the process equipment. Then, there is a problem that the pipe is solidified and in some cases the pipe is blocked. In order to avoid the occurrence of such a problem, a method in which a benzophenone compound and a succinic acid diester are dropped and reacted in a liquid obtained by suspending a metal alkoxide in an appropriate reaction solvent such as toluene has also been performed. However, in such a method, the solvent used has a lower solubility in metal alkoxides than t-butanol, so that not only a long time is required for the reaction, but also the amount of by-products increases, resulting in a decrease in yield. End up.

  Further, when a compound having an electron donating group such as a methoxy group as a substituent is used as the raw material benzophenone compound, the target product cannot be obtained in a high yield even if t-butanol is used as a solvent. For example, Non-Patent Document 2 describes a reaction example using 4,4'-dimethoxybenzophenone as a raw material, but the yield at that time is as low as 47%. In this example, a symmetric compound is used as the benzophenone compound. However, when an asymmetric compound is used, an isomer is formed, so that the yield of the target product is expected to be about 20%.

  The present invention solves the above-mentioned problems, and the following formula (1)

(Wherein R ¹ and R ² are each independently an alkyl group; an alkoxy group; an aralkoxy group; a substituted amino group; a cyano group; an aryl group; a halogen atom; an aralkyl group; a nitrogen atom as a hetero atom; A heterocyclic group in which an atom and a benzene ring are bonded; and one group or atom selected from the group consisting of a condensed heterocyclic group in which an aromatic hydrocarbon ring is bonded to the heterocyclic group, and R ³ is an alkyl group And a and b are each independently an integer of 0 to 5, and when a or b is an integer of 2 to 5, a plurality of R ¹ or R ² present in the molecule may be different from each other. .)
A process for producing an alkylidene succinic acid compound represented by
Including a step of reacting by adding a metal alkoxide dissolved or suspended in ether to a raw material solution containing a benzophenone compound represented by the following formula (2) and a succinic acid diester represented by the following formula (3): It is characterized by.

{Wherein R ¹ , R ² , a and b have the same meanings as in formula (1). }

{Wherein R ³ has the same meaning as in formula (1). }

  According to the method of the present invention, since t-butanol is not used, there is no problem that the solvent adheres and solidifies on the equipment in the post-treatment process. Moreover, although t-butanol is not used, the reaction can be completed at a low temperature for a short time. Even when the metal alkoxide is dissolved or suspended in ether, a large amount of by-products are produced when the benzophenone compound and succinic diester are added to the solution or suspension of the metal alkoxide. In the method of the present invention, the desired product can be obtained in a high yield because the amount of by-products produced is small. Furthermore, according to the present invention, even when a benzophenone compound having an electron donating group such as a methoxy group as a substituent is used as the carbonyl compound, the target product can be obtained in a high yield.

  In the production method of the present invention, the benzophenone compound represented by the above formula (2) and the succinic acid diester represented by the above formula (3) are reacted in the presence of a metal alkoxide to produce an alkylidene succinate represented by the above formula (1). An acid compound is produced.

  The benzophenone compound used as a raw material in the present invention is represented by the following formula (2).

In the above formula (2), R ¹ and R ² each independently represents an alkyl group; an alkoxy group; an aralkoxy group; a substituted amino group; a cyano group; an aryl group; a halogen atom; an aralkyl group; And a heterocyclic group in which the nitrogen atom and a benzene ring are bonded; one group or atom selected from the group consisting of a condensed heterocyclic group in which an aromatic hydrocarbon ring is bonded to the heterocyclic group. Hereinafter, these groups or atoms will be described.

  (I) The alkyl group is preferably an alkyl group having 1 to 4 carbon atoms. Examples of suitable alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a sec-butyl group. , T-butyl group and the like.

  (Ii) The alkoxy group is preferably an alkoxy group having 1 to 5 carbon atoms. Specific examples of suitable alkoxy groups include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, Examples thereof include a sec-butoxy group and a t-butoxy group.

  (Iii) The aralkoxy group is preferably an aralkoxy group having 6 to 10 carbon atoms, and specific examples of suitable aralkoxy groups include phenoxy groups and naphthoxy groups.

  (Iv) The substituted amino group is preferably an alkylamino group, a dialkylamino group, an arylamino group, or a diarylamino group substituted with an alkyl group or an aryl group. Specific examples of suitable substituted amino groups include methylamino group, ethylamino group, phenylamino group, dimethylamino group, diethylamino group, and diphenylamino group.

  (V) The aryl group may have a substituent. The unsubstituted aryl group is preferably an aryl group having 6 to 10 carbon atoms, and examples of suitable groups include a phenyl group and a naphthyl group. As the substituted aryl group, those in which one or two or more hydrogen atoms of the unsubstituted aryl group are substituted with a substituent are preferable. In this case, as the substituent, the same alkyl group, alkoxy group, aryl group, substituted amino group, a halogen atom, an aralkyl group, and a nitrogen atom as described above having a nitrogen atom as a heteroatom are used. Examples include a substituted or unsubstituted heterocyclic group to be bonded, or a substituted aryl group substituted with a substituent such as a condensed heterocyclic group in which an aromatic hydrocarbon ring or an aromatic heterocyclic ring is condensed to the heterocyclic group. .

  (Vi) Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

  (Vii) The aralkyl group is preferably an aralkyl group having 7 to 11 carbon atoms. Examples of suitable aralkyl groups include benzyl group, phenylethyl group, phenylpropyl group, phenylbutyl group and the like.

  (Viii) The heterocyclic group having a nitrogen atom as a hetero atom and bonding the nitrogen atom and the benzene ring may have a substituent. Examples of the substituent include the same substituents as those in the aryl group. In general, the number of carbon atoms constituting the heterocyclic group is preferably 2 to 10, particularly 2 to 6. In the heterocyclic ring, in addition to the nitrogen atom bonded to the benzene ring, a hetero atom may further exist. Although this hetero atom is not specifically limited, an oxygen atom, a sulfur atom, a nitrogen atom, etc. are suitable. Suitable groups for the heterocyclic group include morpholino group, piperidino group, pyrrolidinyl group, piperazinyl group, N-methylpiperazinyl group and the like.

  (Ix) Examples of the condensed heterocyclic group in which an aromatic hydrocarbon ring is bonded to the heterocyclic group (viii) include an indolinyl group and a carbazolyl group.

A and b indicate the number of substitution of R ¹ and ^{R 2} are an integer from 0 to 5. The position at which R ¹ and R ² are bonded is not particularly limited, and the total number is not particularly limited. In addition, when a and b are integers of 2 to 5, each R ¹ (or each R ² ) that will be present in the molecule may be different from each other.

  Specific examples of the benzophenone compound represented by the formula (2) include benzophenone, 4,4′-dimethoxybenzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2,4-dimethylbenzophenone, 2,5-dimethylbenzophenone, 3,4-dimethylbenzophenone, 2-fluorobenzophenone, 4-fluorobenzophenone, 2-chlorobenzophenone, 3-chlorobenzophenone, 4-chlorobenzophenone, 4-bromobenzophenone, 2,4-dichlorobenzophenone 4,4′-dichlorobenzophenone, 3-trifluoromethylbenzophenone, 4-trifluoromethylbenzophenone, 4-methoxybenzophenone, 4,4′-dimethoxybenzophenone, 2-amino Benzophenone, 4-aminobenzophenone, 4,4'-bis (dimethylamino) benzophenone, 4-morpholino-benzophenone, 3-nitro benzophenone, 4-nitro benzophenone.

  As described above, the conventional Stobbe reaction has a problem in that the reaction yield is low when a compound having an electron-donating group is used as a benzophenone compound. In contrast, in the production method of the present invention, the target product can be obtained in high yield even when such a benzophenone compound is used. From the viewpoint of obtaining such a remarkable effect, in the present invention, it is preferable to use a benzophenone compound having at least one electron donating group as a substituent as the benzophenone compound represented by the formula (2). .

Here, the electron donating group means a group that easily emits electrons as compared with a hydrogen atom, and among the groups listed as R ¹ and R ² , groups other than the halogen group in (vi) are electrons. Corresponds to a donating group. That is, in the present invention, among the benzophenone compounds represented by the formula (2), a and b are not both 0 but at least one of R ¹ and / or R ² bonded as a substituent. The compound (vi) having a group other than the halogen group is preferably used. Examples of the benzophenone compound particularly preferably used in the present invention include 4,4′-dimethoxybenzophenone, 4-methylbenzophenone, 2,4-dimethylbenzophenone, 4-methoxybenzophenone, 4,4′-dimethoxybenzophenone, 4 -Aminobenzophenone, 4,4'-bis (dimethylamino) benzophenone, 4-morpholinobenzophenone, etc. can be mentioned.

The succinic diester used as a raw material in the present invention is represented by the formula (3). In the formula (3), R ³ is an alkyl group. Among these, C1-C4 alkyl groups, such as a methyl group, an ethyl group, and t-butyl group, are preferable from availability. Examples of succinic acid diesters that are particularly preferably used in the present invention include dimethyl succinate, diethyl succinate, and di-t-butyl succinate.

  As the metal alkoxide used in the present invention, known ones such as potassium t-butoxide, potassium ethoxide, sodium ethoxide can be used, but potassium t-butoxide is particularly preferred from the viewpoint of ease of handling.

  In the production method of the present invention, when a benzophenone compound and a succinic acid diester are reacted in the presence of a metal alkoxide, a metal alkoxide dissolved or suspended in ether is added to the raw material liquid containing the benzophenone compound and the succinic acid diester. It is important to conduct the reaction. By adopting such a method, the target product can be obtained in high yield without using t-butanol as a solvent. Even when the metal alkoxide is dissolved or suspended in ether, a large amount of by-products are produced when a benzophenone compound and a succinic diester are added to the solution or suspension of the metal alkoxide, resulting in a high yield. Cannot be realized. In the production method of the present invention, the added metal alkoxide is used promptly in the reaction, and free metal alkoxide is unlikely to exist in the reaction system. Therefore, condensation between succinic acid diesters (Claisen reaction) and reaction intermediate anions Side reactions such as attack of benzophenone compounds or succinic diesters on the species are likely to be suppressed. This effect is less pronounced when using a “benzophenone compound with an electron-donating group”, which is less reactive because it is less susceptible to anionic species attack from succinic diesters, and therefore is prone to Claisen reaction. Appears as

  The raw material liquid used in the production method of the present invention is not particularly limited as long as it is a liquid composition containing the benzophenone compound represented by the above formula (1) and a succinic diester, Further, a diluting solvent may be included. The diluting solvent is not particularly limited, but ethers such as diethyl ether and tetrahydrofuran; aromatic hydrocarbons such as toluene and xylene; alcohols such as ethanol and isopropanol; halogenated hydrocarbons such as dichloromethane and chloroform; etc. Is mentioned. Among these, it is particularly preferable to use the same ether as that used for suspending or dissolving the metal alkoxide because the reaction system is not complicated and the subsequent treatment is simplified.

  The ratio of the benzophenone compound and the succinic acid diester derivative contained in the raw material liquid is not particularly limited, but from the viewpoint of reaction efficiency, 0.5 to 1.5 mol, particularly 0. It is preferable to use 9 to 1.3 mol. Moreover, when using a dilution solvent, it is suitable that the usage-amount of the dilution solvent shall be 50-5000 mass parts with respect to a total of 100 mass parts of a benzophenone compound and a succinic-acid diester derivative, especially 100-1000 mass parts. .

  In the production method of the present invention, the metal alkoxide is dissolved or suspended in ether and added to the raw material liquid. At this time, as the ether, known ones such as tetrahydrofuran, diethyl ether, diisopropyl ether, dibutyl ether, dioxane, ethylene glycol, ethylene glycol dimethyl ether can be used, but it is particularly preferable to use tetrahydrofuran that dissolves metal alkoxide relatively well. It is. An ether solution of a metal alkoxide (in this case, the metal alkoxide does not have to be completely dissolved, and a part thereof may be in a suspended state) or an ether suspension (in this case, a part of the metal alkoxide is It may be dissolved.) Can be prepared by mixing a metal alkoxide and ether and stirring as necessary. At this time, it is preferable that the mixing ratio of both is 100 to 5000 parts by mass, particularly 300 to 3000 parts by mass of ether with respect to 100 parts by mass of the metal alkoxide. In addition, from the viewpoint of operability, the liquid temperature when preparing the solution or suspension is preferably 10 to 50 ° C.

  In addition, the amount of the metal alkoxide ether solution or ether suspension (hereinafter also collectively referred to as metal alkoxide liquid) used is that of the metal alkoxide added to 1 mol of the benzophenone compound from the viewpoint of reaction efficiency and economy. Expressed in terms of the total number of moles, 0.8 to 2.0 moles, particularly 1.0 to 1.5 moles is preferred.

  The method for adding the metal alkoxide liquid to the raw material liquid is not particularly limited. For example, the metal alkoxide liquid can be suitably carried out by dropping the metal alkoxide liquid into the raw material liquid adjusted to a predetermined temperature in advance. At this time, the raw material liquid is preferably stirred. Further, the dropping rate of the metal alkoxide liquid is expressed as the number of moles of metal alkoxide added in 1 minute per 1 mole of benzophenone compound in the raw material liquid, and is 0.003 to 1 mol / min, particularly 0.01 to 0.3 mol. It is preferable to set the speed so as to be / min. When a metal alkoxide is added to the raw material liquid, the reaction starts and the reaction proceeds. The reaction temperature, that is, the temperature of the reaction solution during the addition of the metal alkoxide solution and until the completion of the reaction after the completion of the dropping is 100 ° C. or less, particularly 20 to 70 ° C., from the viewpoint of suppressing by-product formation. It is preferable to do this. Moreover, although reaction time is based also on temperature, it is about 30 minutes-about 24 hours normally. The completion of the reaction can be confirmed by sampling a small amount of the reaction solution and analyzing it by high performance liquid chromatography or gas chromatography.

  After completion of the reaction, the target product may be separated from the reaction solution after the temperature of the reaction solution is set to a temperature around room temperature. The method for separating the target product can be suitably performed as follows. That is, first, water and a water-insoluble organic solvent (for example, toluene) are added to the reaction solution to extract the unreacted raw material into the organic solvent phase, and then the aqueous phase and the organic phase are separated and the aqueous phase containing the target product Recover. Next, an acid (for example, hydrochloric acid) is added to the aqueous phase to make it acidic, and then the target product is extracted with an appropriate organic solvent (for example, ethyl acetate), and the target product is separated by removing the extraction solvent from the extract. be able to. The target product thus separated can be purified by column chromatography using silica gel or the like, distillation, recrystallization or the like, if necessary.

  In the present invention, a compound having a symmetric structure as a raw material benzophenone compound (in other words, in the formula (2), when a = b = 0 or both a and b are not 0, the substituent Is a compound in which two benzene rings having a mirror image are in a mirror image relationship), the main product is one alkylidene succinic acid compound represented by the above formula (1). On the other hand, a compound having an asymmetric structure as a raw material benzophenone compound (in other words, when a and b are not 0 in formula (2), the two benzene rings having substituents are not in a mirror image relationship) In the case of a compound), in addition to the alkylidene succinic acid compound represented by the formula (1), an equivalent amount of the compound represented by the following formula (1 ′) which is an isomer thereof is produced.

{Wherein R ¹ , R ² , R ³ , a and b have the same meanings as in formula (1). }
Therefore, the yield when an asymmetric benzophenone compound is used as a raw material does not greatly exceed 50%. The above formula (1 ′) is also a useful compound, and can be used, for example, as a raw material for synthesizing photochromic compounds. However, when only the compound represented by the formula (1) is the target product, the two isomers are separated. Is preferred. As a method for separating isomers, column chromatography, recrystallization and the like can be employed. Depending on the kind of the compound, it may be difficult to separate by such a method. In that case, the compound may be converted into a separable derivative and then separated.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1
300 g (2.71 mol) of potassium t-butoxide and 3000 ml of tetrahydrofuran were sufficiently mixed and dissolved to prepare a metal alcoside solution. Separately, 500 g (2.36 mol) of 4-methoxybenzophenone and 472 g (2.71 mol) of diethyl succinate are added to 3800 ml of tetrahydrofuran as a diluting solvent, and thoroughly mixed at room temperature to dissolve the raw material components, thereby starting the raw material. A liquid was prepared. Then, after heating up a raw material liquid to 50 degreeC, the metal alkoxide liquid was dripped over 30 minutes, stirring, keeping liquid temperature in the range of 50-60 degreeC, and it was made to react at 60 degreeC for 3 hours. After completion of the reaction, the reaction solution was cooled to room temperature, water and toluene were added to separate the toluene layer, hydrochloric acid was added to the remaining aqueous layer to adjust to pH 1, and the product was extracted using ethyl acetate as an extraction solvent. . Thereafter, the oily substance obtained by concentrating the extract was purified by column chromatography using silica gel to obtain 770 g of a colorless transparent bowl-like solid. By analysis by ¹ H-NMR, the solid is a mixture of two isomers represented by (C ₆ H ₅ ) (4-OMeC ₆ H ₅ ) C═C (CO ₂ Et) CH ₂ CO ₂ H It was confirmed that the mixing ratio was about 1: 1. The yield of the mixture of the two isomers was 96%, and the yield of the target product was about 48%.

Example 2
A metal alkoxide solution was prepared by thoroughly mixing and suspending 300 g (2.71 mol) of potassium t-butoxide and 6000 ml of diisopropyl ether. Furthermore, 690 g (2.36 mol) of 3-bromo-4-methoxybenzophenone and 472 g (2.71 mol) of diethyl succinate were added to 3800 ml of diisopropyl ether as a diluent solvent, and mixed well at room temperature to prepare a raw material solution separately. did. Using these solutions, the reaction, treatment and purification were carried out in the same manner as in Example 1, and (C ₆ H ₅ ) (3-Br-4-OMeC ₆ H ₅ ) C═C (CO ₂ Et) CH ₂ CO _As a mixture of two isomers represented by ₂ H, 940 g of a colorless transparent bowl-shaped solid (yield as a mixture: 95%, target product yield: about 48%) was obtained.

Example 3
A metal alkoxide solution was prepared by adding 300 g (2.71 mol) of potassium t-butoxide to 3000 ml of tetrahydrofuran and thoroughly mixing and dissolving. Further, 570 g (2.36 mol) of 4,4-dimethoxybenzophenone and 472 g (2.71 mol) of diethyl succinate were added to 3800 ml of tetrahydrofuran, and mixed and dissolved sufficiently at room temperature to prepare a raw material solution. Using these solutions, the reaction, treatment and purification were carried out in the same manner as in Example 1, and 820 g of a white solid represented by (4-OMeC ₆ H ₅ ) ₂ C═C (CO ₂ Et) CH ₂ CO ₂ H ( Yield: 94%).

Example 4
A metal alkoxide solution was prepared by adding 300 g (2.71 mol) of potassium t-butoxide to 3000 ml of tetrahydrofuran and thoroughly mixing and dissolving. Separately, 531 g (2.36 mol) of 4-dimethylaminobenzophenone and 434 g (2.71 mol) of dimethyl succinate were sufficiently mixed at room temperature to prepare a raw material solution. Using these solutions, the reaction, treatment and purification were carried out in the same manner as in Example 1, and (C ₆ H ₅ ) (4-N (Me) ₂ C ₆ H ₅ ) C═C (CO ₂ Me) CH ₂ 760 g of a colorless transparent bowl-like solid represented by CO ₂ H (yield as a mixture: 95%, yield of the target product: about 48%) was obtained.

Comparative Example 1
300 g (2.71 mol) of potassium t-butoxide was added to 3000 ml of t-butanol, and thoroughly mixed and dissolved to prepare a metal alkoxide solution. Further, 500 g (2.36 mol) of 4-methoxybenzophenone and 472 g (2.71 mol) of diethyl succinate were added to 3800 ml of t-butanol, and sufficiently mixed and dissolved at room temperature to prepare a raw material solution. After raising the temperature of the metal alkoxide solution to 50 ° C., the raw material solution was added dropwise while maintaining the solution temperature in the range of 50 to 60 ° C., and reacted at the reflux temperature for 3 hours. After completion of the reaction, the reaction mixture was cooled to room temperature, and t-butanol was distilled off under reduced pressure. However, this caused a problem that the distillation tube was blocked many times. After distilling off, water and toluene were added to separate the toluene layer, hydrochloric acid was added to the remaining aqueous layer to adjust to pH 1, and the product was extracted using ethyl acetate as an extraction solvent and concentrated to give an oily product. Got. The obtained oily substance is purified by column chromatography using silica gel and expressed as (C ₆ H ₅ ) (4-OMeC ₆ H ₅ ) C═C (CO ₂ Et) CH ₂ CO ₂ H 2 As a mixture of various isomers, 633 g of a colorless transparent bowl-like solid (yield as a mixture: 79%, yield of the target product: about 39%) was obtained.

Comparative Example 2
A metal alkoxide solution was prepared by adding 300 g (2.71 mol) of potassium t-butoxide to 3000 ml of toluene and thoroughly mixing and suspending. Further, 500 g (2.36 mol) of 4-methoxybenzophenone and 472 g (2.71 mol) of diethyl succinate were added to 3800 ml of toluene, and thoroughly mixed and dissolved at room temperature to prepare a raw material solution. After raising the temperature of the metal alkoxide solution to 50 ° C., the raw material solution was added dropwise while maintaining the solution temperature in the range of 50 to 60 ° C., and reacted at the reflux temperature for 3 hours. The obtained reaction solution is treated and purified in the same manner as in Example 1 to express (C ₆ H ₅ ) (4-OMeC ₆ H ₅ ) C═C (CO ₂ Me) CH ₂ CO ₂ H. As a mixture of two isomers, 602 g of a colorless transparent bowl-like solid (yield as a mixture: 75%, yield of the target product: about 37%) was obtained.

Claims (2)

Following formula (1)

(Wherein R ¹ and R ² are each independently an alkyl group; an alkoxy group; an aralkoxy group; a substituted amino group; a cyano group; an aryl group; a halogen atom; an aralkyl group; a nitrogen atom as a hetero atom; A heterocyclic group in which an atom and a benzene ring are bonded; and one group or atom selected from the group consisting of a condensed heterocyclic group in which an aromatic hydrocarbon ring is bonded to the heterocyclic group, and R ³ is an alkyl group And a and b are each independently an integer of 0 to 5, and when a or b is an integer of 2 to 5, a plurality of R ¹ or R ² present in the molecule may be different from each other. .)
A method for producing an alkylidene succinic acid compound represented by formula (2), wherein a benzophenone compound represented by the following formula (2) and a succinic acid diester represented by the following formula (3) are dissolved or suspended in ether: A method comprising a step of reacting by adding a metal alkoxide formed.

{Wherein R ¹ , R ² , a and b have the same meanings as in formula (1). }

{Wherein R ³ has the same meaning as in formula (1). } The method according to claim 1, wherein the benzophenone compound represented by the formula (2) is a benzophenone compound having at least one electron donating group as a substituent.