WO2018097150A1

WO2018097150A1 - Epoxy compound production method

Info

Publication number: WO2018097150A1
Application number: PCT/JP2017/041914
Authority: WO
Inventors: 英良土屋
Original assignee: 帝人ファーマ株式会社
Priority date: 2016-11-24
Filing date: 2017-11-22
Publication date: 2018-05-31
Also published as: TW201825470A

Abstract

With a step in which a phosphoric acid compound and/or a phosphonic acid compound, a group 6 metal compound, a phase transfer catalyst, and hydrogen peroxide are added to and reacted with 3-cyclopentene in which the 1-position is substituted by a C_{1-C6 alkoxycarbonyl group, a benzyloxycarbonyl group, a C1-C6 alkylcarbonyl group, a benzyloxycarbonyl group, a C1-C6 alkyl group or a benzoyl group (these substituents may be further substituted by specific substituents), this production method produces a corresponding epoxy compound. From a 3-cyclopentene in which the 1-position is monosubstituted with a specific substituent, a corresponding epoxy compound with high stereoselectivity can be produced.}

Description

Method for producing epoxy compound

The present invention relates to a method for stereoselectively epoxidizing a double bond of a mono-substituted 3-cyclopentene compound at the 1-position.

Conventionally, epoxidation of 1-position mono-substituted 3-cyclopentene compounds has low stereoselectivity and has been a problem as an industrial production method.

Specifically, metachloroperbenzoic acid (mCPBA) is known as an epoxidizing agent for olefins, but epoxidation of mono-substituted 3-cyclopentene compounds is not highly stereoselective. For example, when the substituent at the 1-position is a methyl ester group, the ratio is 3: 1 (Non-Patent Document 1), and when the substituent is a benzyloxymethyl group, the ratio is 3: 2 (Non-Patent Document 2). In the case of a tert-butyldimethylsilyloxymethyl group, the ratio is 8: 1. Although the stereoselectivity is improved (Non-patent Document 3), in addition to using an expensive silyl compound, the molecular weight of the substrate increases. This increases the amount of waste and is not suitable for an industrial manufacturing method from the viewpoint of process conversion efficiency (Atom Economy).

In addition, a method for epoxidizing a cyclohexene compound using hydrogen peroxide as an oxidizing agent in the presence of a quaternary ammonium hydrogen sulfate salt, a phosphoric acid compound or a phosphonic acid compound, and a Group 6 metal compound is known (Patent Document 1). ). However, this reaction is a multifunctional substrate in which the steric pathway to the olefin plane of the oxidant is controlled by replacing the two positions at positions 1 and 2 of the cyclohexene ring of the reaction substrate with an allyl ester group in the syn configuration. (Details will be described later).

On the other hand, epoxidation reaction with high stereoselectivity of mono-substituted cyclopentene ring is not known.

JP 2008-94741 A

An object of the present invention is to provide a method for producing a corresponding epoxy compound from a mono-substituted 3-cyclopentene compound with high anti / syn stereoselectivity.

As a result of intensive studies by the present inventors, as a phase transfer catalyst, for example, a quaternary ammonium salt, a phosphoric acid compound and / or a phosphonic acid compound, and a Group 6 metal compound are used as a catalyst, and the 1-position is mono-substituted with a specific substituent. It was found that by reacting the 3-cyclopentene compound with hydrogen peroxide, the corresponding epoxy compound can be produced stereoselectively in a high yield. The inventors of the present invention have continued research based on such knowledge and have completed the present invention.

That is, the present invention includes a step of reacting a compound represented by the formula (1) by adding a phosphoric acid compound and / or a phosphonic acid compound, a Group 6 metal compound, a phase transfer catalyst, and hydrogen peroxide, and reacting them. It is a manufacturing method of the compound represented by 2).

Here, R in the formula (1) and the formula (2) is a C ₁ -C ₆ alkoxy group which may be substituted with 1 to 2 (phenyl group and / or halogen atom), 1 to 2 C 1 _~ C ₄ alkyl optionally benzyloxy group optionally substituted with a group, one to two (phenyl group and / or halogen atom) with optionally substituted C _{1 to} C ₆ alkyl group or 1, Represents a phenyl group which may be substituted by ˜2 C ₁ -C ₄ alkyl groups;

According to the present invention, a corresponding epoxy compound can be produced with high anti / syn stereoselectivity and high yield from the reaction of 3-cyclopentene compound monosubstituted with a specific substituent at the 1-position with hydrogen peroxide. .

The figure which displayed the molecular dynamics calculation result of the most stable conformation of (1R, 2S) -4-cyclohexene-1,2-dicarboxylate diallyl. The cyclohexene ring is on the left side of the figure. The figure which displayed the molecular dynamics calculation result of the most stable conformation of ethyl 3-cyclopentene-1-carboxylate. The cyclopentene ring is on the right side of the figure.

In the present invention, the compound represented by the above formula (1) is oxidized using hydrogen peroxide in the presence of a phosphoric acid compound and / or a phosphonic acid compound, a group 6 metal compound, and a phase transfer catalyst, and the above formula (2). This is a method for producing a compound represented by

In the formula (1) and the formula (2), R is a C ₁ -C ₆ alkoxy group which may be substituted with 1 to 2 (phenyl group and / or halogen atom), 1 to two C _{1 ~} C ₄ alkyl group which may be substituted benzyloxy group, 1-2 (phenyl group and / or a halogen atom) alkyl _~ C ₆ optionally C ₁ optionally substituted with Or a phenyl group optionally substituted by 1 to 2 C ₁ -C ₄ alkyl groups. Among these, R is preferably a C ₁ -C ₆ alkoxy group, a benzyloxy group, a C ₁ -C ₆ alkyl group, or a phenyl group, and particularly preferably a C ₁ -C ₆ alkoxy group.

As the hydrogen peroxide source in the production method of the present invention, for example, urea-hydrogen peroxide and hydrogen peroxide water are used. Of these, hydrogen peroxide water is inexpensive and non-corrosive, and the by-product after the reaction is water. Therefore, the environmental load is small and it is excellent for industrial use.

When hydrogen peroxide is used in the production method of the present invention, the concentration thereof is not limited, but is generally selected from the range of 1 to 80%, preferably 20 to 80%.

The amount of hydrogen peroxide used at that time is not limited, but it is generally selected from the range of 0.8 to 3.0 equivalents, preferably 1.0 to 2.0 equivalents, relative to the olefins.

As the phase transfer catalyst used in the production method of the present invention, a quaternary ammonium salt is suitable.

Such quaternary ammonium salts include, for example, methyltri n-octylammonium chloride, tetra n-butylammonium chloride, tetra n-butylammonium bromide, tetra n-butylammonium hydroxide, tetra n-hexylammonium hydrogen sulfate, tetrahydrogen hydrogen sulfate. n-Octylammonium hydrogen, methyltri-n-octylammonium hydrogensulfate, tetra-n-butylammonium hydrogensulfate, and ethyltri-n-octylammonium hydrogensulfate are preferred, for example, tetra-n-butylammonium hydrogensulfate and methyltri-n-octylammonium hydrogensulfate A quaternary ammonium hydrogen sulfate salt such as These quaternary ammonium salts may be used alone or in combination of two or more. The amount used is generally selected from the range of 0.0001 to 10 mol%, preferably 0.01 to 5 mol%, based on the olefins of the substrate.

As the group 6 metal in the group 6 metal compound used in the production method of the present invention, molybdenum or tungsten is preferable.

When the Group 6 metal is molybdenum, the molybdenum compound used in the production method of the present invention is a compound that generates molybdate anions in water. For example, molybdic acid, molybdenum oxide, molybdenum sulfide, molybdenum chloride, phosphomolybdic acid, molybdic acid Ammonium, potassium molybdate, and sodium molybdate.

When the Group 6 metal is tungsten, the tungsten compound used in the production method of the present invention is a compound that generates a tungstate anion in water. For example, tungstic acid, tungsten oxide, tungsten sulfide, tungsten chloride, phosphotungstic acid, tungstic acid Ammonium, potassium tungstate (including hydrate), and sodium tungstate (including hydrate).

As the Group 6 metal compound used in the present invention, molybdic acid, molybdenum oxide, phosphomolybdic acid, molybdate, tungstic acid, tungsten oxide, phosphotungstic acid, and tungstate are preferable. Of these, molybdate and tungstate are preferable, and tungstate is more preferable, and sodium tungstate is particularly preferable, but sodium tungstate dihydrate is most preferable.

These group 6 metal compounds may be used alone or in combination of two or more. The amount used is generally selected from the range of 0.0001 to 20 mol%, preferably 0.01 to 20 mol%, based on the olefins of the substrate.

In the production method of the present invention, it is necessary to use a phosphoric acid compound and / or a phosphonic acid compound as a cocatalyst in order to improve the catalytic activity. Such phosphoric acid compounds and / or phosphonic acid compounds include phosphoric acid, polyphosphoric acid, pyrophosphoric acid, α-aminomethylphosphonic acid, α-aminoethylphosphonic acid, nitrilotris (methylenephosphonic acid), phenylphosphonic acid, and these Sodium salts and potassium salts are mentioned, among which phosphoric acid and phenylphosphonic acid are preferable. The amount of the phosphoric acid compound and / or phosphonic acid compound used is generally selected from the range of 0.0001 to 20 mol%, preferably 0.01 to 20 mol%, based on the olefins of the substrate.

In addition, although sulfates such as sodium sulfate, sodium sulfate decahydrate, lithium sulfate, potassium sulfate, ammonium sulfate, or magnesium sulfate may be used as the additive, such an additive is the stereoselective object of the present invention. There is no particular influence on the properties, and forms without using such additives are also included in the embodiments of the present invention.

The solvent used in the production method of the present invention is not particularly limited, and examples thereof include toluene, xylene, chloroform, dichloromethane, 1,2-dichloroethane, acetonitrile, hexane, and heptane. In addition, a mixture of these solvents and water can be used, and the reaction can be performed without using a solvent, but a reaction without using a solvent is particularly preferable.

In the production method of the present invention, the epoxidation reaction is usually performed in the range of 20 to 100 ° C, preferably in the range of 20 to 70 ° C. However, when tetra-n-butylammonium hydrogen sulfate is used as the quaternary ammonium salt, the range of 40 to 60 ° C. is preferable.

In this example, the following equipment was used for the analysis.
Gas chromatography (GC)
Apparatus: Agilent Technologies, Inc. 7890B GC system column: DB-624 (length: 30.0 m, inner diameter: 0.32 mm, film thickness: 1.80 μm)
Inlet temperature: 180 ° C
Detector temperature: 260 ° C
Initial temperature: 80 ° C
Initial holding time: 2 minutes Temperature rising rate: 18 ° C / min Final temperature: 170 ° C
Final retention time: 24.8 minutes Split ratio: 1:10
Carrier gas: Helium carrier gas Flow rate: 2 mL / min
Nuclear magnetic resonance (NMR)
Equipment: Bruker Ultra Shield (400 MHz)
Software: Bruker TopSpin

Molecular mechanics <br/> Software: Schrödinger "Maestro" version 10.7
Calculation method: Advanced mode mixed-torstional / low-mode samples Conformation search (in vacuum) by function (molecular mechanics calculation)
Calculation conditions: Use the default value of the above mode (in vacuum)
Force field: OPLS3

[Example 1]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, ethyl 3-cyclopentene-1-carboxylate (10.01 g, 71.38 mmol), sodium tungstate dihydrate (235 mg, 0.71 mmol), phenylphosphonic acid (56 mg, 0.36 mmol) ), And tetra n-butylammonium hydrogen sulfate (242 mg, 0.71 mmol). After raising the temperature of the reaction solution to 50 ° C., 30% aqueous hydrogen peroxide (9.48 mL, 92.79 mmol) was added over 4 hours. After stirring at 50 ° C. for 1 hour, isopropyl acetate (30 mL) was added and the aqueous layer was removed. The organic layer was washed successively with 1 mol / L aqueous sodium thiosulfate solution (28.6 mL) and 10% brine (22.0 mL). The obtained organic layer was concentrated under reduced pressure to obtain the title compound (10.40 g, anti / syn = 93/7). Yield 93%.
¹ H-NMR (400 MHz, CDCl ₃ ) δ 1.25 (t, J = 7.2 Hz, 3H), 1.89 (dd, J = 9.6, 14.0 Hz, 2H), 2.35 (dd , J = 8.0, 14.0 Hz, 2H), 2.59-2.68 (m, 1H), 3.52 (s, 2H), 4.13 (q, J = 7.2 Hz, 2H) .
FIG. 1 shows the most stable conformation of the compound (1) which is the starting material described in Example 1 of Patent Document 1 by molecular mechanics calculation. Although the configuration of the two allyl ester groups in this compound is not specified, the two allyl groups in compound (1) are determined from the three-dimensional structure of product (2) and compound (3). It is clear that the steric configuration of the ester group was a syn configuration.

As shown in FIG. 1, the most stable conformation of compound (1) has two of the same energy level (potential energy: both 23.353 kcal / mol). Even in the case of conformation, one of the substituents at the 1,2-position of the cyclohexene ring is always in the axial position, and the side on which the substituent exists is present with respect to the ring surface containing the double bond of the cyclohexene ring. Will be crowded in three dimensions. Therefore, it is strongly suggested that the oxidizing agent as an epoxidizing agent is selectively approached from the surface opposite to the substituent, and therefore high anti / syn stereoselectivity can be expected.

On the other hand, FIG. 2 shows the most stable conformation of ethyl 3-cyclopentene-1-carboxylate used in Example 1 as an example of the starting material in the present invention by molecular mechanics calculation under the same conditions (potential energy: -31.69 kcal / mol). Since the ethyl ester group, which is the 1-position substituent, is located in parallel with the cyclopentene ring, it strongly suggests that there is almost no steric difference on either side of the ring surface containing the double bond of the cyclopentene ring. Is done. That is, from this calculation result, there was almost no difference in the steric environment between the Re plane and the Si plane of the epoxidation reaction, and therefore high anti / syn stereoselectivity could not be expected for the epoxidation reaction of the present invention. In fact, it was found that there was unexpectedly high stereoselectivity.
[Example 2]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, ethyl 3-cyclopentene-1-carboxylate (10.00 g, 71.34 mmol), sodium molybdate dihydrate (174 mg, 0.72 mmol), phenylphosphonic acid (57 mg, 0.36 mmol) ), And tetra n-butylammonium hydrogen sulfate (242 mg, 0.71 mmol). After raising the temperature of the reaction solution to 50 ° C., 30% aqueous hydrogen peroxide (9.48 mL, 92.79 mmol) was added over 2.5 hours. After stirring at 50 ° C. for 46 hours, isopropyl acetate (30 mL) was added and the aqueous layer was removed. The organic layer was washed successively with 1 mol / L aqueous sodium thiosulfate solution (28.5 mL) and 10% brine (22.0 mL). The obtained organic layer was concentrated under reduced pressure to obtain the title compound (9.12 g, anti / syn = 89/11). Yield 82%.

[Example 3]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, ethyl 3-cyclopentene-1-carboxylate (20.00 g, 142.67 mmol), sodium tungstate dihydrate (941 mg, 2.85 mmol), phenylphosphonic acid (226 mg, 1.43 mmol) ), Methyl tri-n-octylammonium hydrogensulfate (1.33 g, 2.85 mmol), and sodium sulfate (6.08 g, 42.80 mmol) were added, and 30% aqueous hydrogen peroxide (9.48 mL, 92.79 mmol) was added. Added over 3 hours at room temperature. After stirring at 20-30 ° C. for 19 hours, isopropyl acetate (60 mL) was added and the aqueous layer was removed. The organic layer was washed successively with 10% aqueous sodium thiosulfate solution (67.67 g) and 10% brine (44 mL). The obtained organic layer was concentrated under reduced pressure to obtain the title compound (23.96 g, anti / syn = 92/8). Yield 108%.

[Example 4]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, ethyl 3-cyclopentene-1-carboxylate (1.00 g, 7.13 mmol), sodium tungstate dihydrate (47 mg, 0.14 mmol), phenylphosphonic acid (58 mg, 0.07 mmol) ), Methyltri-n-octylammonium chloride (58 mg, 0.14 mmol), and sodium sulfate (0.304 g, 2.14 mmol) were added, and 30% aqueous hydrogen peroxide (0.95 mL, 9.27 mmol) was added at room temperature. The mixture was added over 5 hours and stirred at 23-24 ° C. for 22 hours and at 47 ° C. for 3 hours. Evaluation was made at the end point of the reaction without post-treatment. The quantitative yield by gas chromatography was 84%, and the production ratio was anti / syn = 89/11.

[Example 5]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, ethyl 3-cyclopentene-1-carboxylate (10.00 g, 71.34 mmol), sodium tungstate dihydrate (471 mg, 1.43 mmol), phosphoric acid (content 85%, 82 mg, 0.71 mmol), methyltri-n-octylammonium hydrogensulfate (665 mg, 1.43 mmol), and sodium sulfate (3.04 g, 21.40 mmol) were added, and 30% aqueous hydrogen peroxide (9.48 mL, 92.79 mmol) was added. Was added at room temperature over 2 hours. After stirring at 20-30 ° C. for 16.5 hours, isopropyl acetate (30 mL) was added and the aqueous layer was removed. The organic layer was washed successively with 1 mol / L aqueous sodium thiosulfate solution (21.4 mL) and 10% brine (20.0 mL). The obtained organic layer was evaluated by gas chromatography. The quantitative yield was 83%, and the production ratio was anti / syn = 87/13.

[Example 6]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, isopropyl acetate (300 mL), ethyl 3-cyclopentene-1-carboxylate (125.02 g, 891.82 mmol), sodium tungstate dihydrate (2.94 g, 8.92 mmol), phenyl Phosphonic acid (0.71 g, 4.46 mmol) and tetra n-butylammonium hydrogen sulfate (3.03 g, 8.92 mmol) were added. After raising the temperature of the reaction solution to 50 ° C., 30% aqueous hydrogen peroxide (118.41 mL, 1159.37 mmol) was added over 5.5 hours. After stirring at 50 ° C. for 21 hours, isopropyl acetate (100 mL) was added and the aqueous layer was removed. The organic layer was washed successively with 1 mol / L aqueous sodium thiosulfate solution (357 mL) and 10% brine (250 mL). The obtained organic layer was concentrated under reduced pressure to obtain the title compound (113.38 g, anti / syn = 94/6). Yield 81%.

[Example 7]
Synthesis of ethyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, toluene (2.0 mL), ethyl 3-cyclopentene-1-carboxylate (1.00 g, 7.13 mmol), sodium tungstate dihydrate (47 mg, 0.14 mmol), phenylphosphone Acid (11 mg, 0.07 mmol), methyltri-n-octylammonium hydrogensulfate (66 mg, 0.14 mmol), and sodium sulfate (304 mg, 2.14 mmol) were added and 30% aqueous hydrogen peroxide (0.95 mL, 9.4). 27 mmol) was added at room temperature over 1.5 hours and stirred at 20-30 ° C. for 46 hours. No post-treatment was performed, and the reaction end point was evaluated by gas chromatography. The production ratio was anti / syn = 87/13.

[Example 8]
Synthesis of isopropyl (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate

Under a nitrogen stream in a reaction vessel, isopropyl 3-cyclopentene-1-carboxylate (10.00 g, 64.87 mmol), sodium tungstate dihydrate (428 mg, 1.30 mmol), phenylphosphonic acid (103 mg, 0.65 mmol) ), And tetra n-butylammonium (441 mg, 1.30 mmol). After raising the temperature of the reaction solution to 50 ° C., 30% aqueous hydrogen peroxide (8.61 mL, 84.33 mmol) was added over 4 hours. After stirring at 50 ° C. for 2 hours, isopropyl acetate (30 mL) was added and the aqueous layer was removed. The organic layer was washed sequentially with 1 mol / L aqueous sodium thiosulfate solution (19.5 mL) and 10% brine (22 mL). The obtained organic layer was concentrated under reduced pressure to obtain the title compound (11.92 g, anti / syn = 94/6). Yield 103%.
¹ H-NMR (400 MHz, CDCl ₃ ) δ 1.23 (d, J = 6.4 Hz, 6H), 1.89 (dd, J = 8.8, 14.4 Hz, 2H), 2.64-2 .70 (m, 3H), 3.46 (s, 2H), 4.99 (m, 1H).

[Example 9]
Synthesis of (1R, 3s, 5S) -6-oxabicyclo [3.1.0] hexane-3-carboxylate isobutyl

Under a nitrogen stream in a reaction vessel, isobutyl 3-cyclopentene-1-carboxylate (1.00 g, 5.95 mmol), sodium tungstate dihydrate (39 mg, 0.12 mmol), phenylphosphonic acid (9.4 mg, 0 0.06 mmol), methyl tri-n-octylammonium hydrogensulfate (55 mg, 0.12 mmol), and sodium sulfate (254 mg, 1.78 mmol) were added, and 30% aqueous hydrogen peroxide (0.79 mL, 7.73 mmol) was added at room temperature. Added over 1 hour. After stirring at 20-30 ° C. for 17.5 hours, 1 mol / L aqueous sodium thiosulfate solution (1.8 mL) and isopropyl acetate (10 mL) were added, and the aqueous layer was removed. The aqueous layer was re-extracted with isopropyl acetate (10 mL) and the combined organic layers were washed with water (5 mL). The obtained organic layer was evaluated by gas chromatography. The production ratio was anti / syn = 91/9.
[Comparative Example 1]

Under a nitrogen stream in a reaction vessel, 3-cyclopentene-1-methylbenzoate (1.00 g, 7.13 mmol), sodium tungstate dihydrate (23.5 mg, 0.07 mmol), phenylphosphonic acid (5.7 mg, 0.04 mmol), and tetra n-butylammonium hydrogen sulfate (24.4 mg, 0.07 mmol) were added. After raising the temperature of the reaction solution to 50 ° C., 30% aqueous hydrogen peroxide (0.95 mL, 9.27 mmol) was added over 2 hours. After stirring at 50 ° C. for 2 hours, isopropyl acetate (3 mL) was added and the aqueous layer was removed. The organic layer was washed with 1 mol / L aqueous sodium thiosulfate solution (2.9 mL), and the obtained organic layer was evaluated by gas chromatography. The production ratio was anti / syn = 64/36.

This result shows that when the substituent at the 1-position of the cyclopentene ring in the formula (1) is a benzoyloxymethyl group instead of R (C═O) —, the anti / syn stereoselection of the epoxidation reaction of the cyclopentene ring It shows that the sex is significantly reduced.

The method for producing an epoxy compound of the present invention is used, for example, in the chemical industry including the pharmaceutical manufacturing industry.

Claims

The compound represented by the formula (1) is represented by the formula (2) including a step of adding a phosphoric acid compound and / or a phosphonic acid compound, a group 6 metal compound, a phase transfer catalyst, and hydrogen peroxide to react. A method for producing a compound. Here, R in the formula (1) and the formula (2) is a C 1 -C 6 alkoxy group which may be substituted with 1 to 2 (phenyl group and / or halogen atom), 1 to 2 C 1 ~ C 4 alkyl optionally benzyloxy group optionally substituted with a group, one to two (phenyl group and / or halogen atom) with optionally substituted C 1 to C 6 alkyl group or 1, Represents a phenyl group which may be substituted by ˜2 C 1 -C 4 alkyl groups;
The production method according to claim 1, wherein R is a C 1 -C 6 alkoxy group, a benzyloxy group, a C 1 -C 6 alkyl group, or a phenyl group.
The production method according to claim 1, wherein R is a C 1 -C 6 alkoxy group.
The production method according to any one of claims 1 to 3, wherein the phosphoric acid compound and / or the phosphonic acid compound is phenylphosphonic acid or phosphoric acid.
The production method according to any one of claims 1 to 4, wherein the Group 6 metal compound is tungstate or molybdate.
The production method according to any one of claims 1 to 4, wherein the Group 6 metal compound is sodium tungstate dihydrate.
The production method according to any one of claims 1 to 6, wherein the phase transfer catalyst is a quaternary ammonium salt.
The production method according to claim 7, wherein the quaternary ammonium salt is a quaternary ammonium hydrogen sulfate salt.
The production method according to claim 8, wherein the quaternary ammonium hydrogen sulfate salt is tetra-n-butylammonium hydrogensulfate or methyltri-n-octylammonium hydrogensulfate.