A method for synthesizing xanthene dye

Abstract

The present invention discloses a method for synthesizing a xanthene dye, comprising the following steps: (1) in the presence of a base and a catalyst, an esterification reagent is used to perform an esterification reaction on the hydroxyl group on sulfonyl fluorescein to obtain an intermediate A; and (2) in the presence of a base and a nickel catalyst, the intermediate A is subjected to a C-N bond coupling reaction with an amine compound to obtain a target xanthene dye 2. The method for synthesizing the xanthene dye of the present invention avoids the need to first chlorinate sulfonyl fluorescein with a strongly acidic and highly corrosive chlorination reagent, such as phosphorus oxychloride, phosphorus pentachloride, or thionyl chloride, as in traditional synthesis methods. This not only reduces the generation of a large amount of strongly acidic gas, but also reduces corrosion to production equipment. In addition, the nickel-catalyzed C-N coupling reaction is mild, greatly reducing the reaction temperature and energy consumption, making this synthesis method more suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of color filters, and in particular to a method for synthesizing a xanthene dye. Background Art

[0002] Color liquid crystal displays (LCDs) transmit white light from a backlight through the color filters, thereby coloring the image and displaying a color image. Therefore, high transparency is a fundamental requirement for color filters. However, traditional pigment-based color pastes, due to the poor solubility of pigment molecules, often form large clusters in the photoresist. This scatters the backlight, reducing the contrast of the color filter and making it difficult to meet the requirements of the higher-performance new color LCDs.

[0003] Compared to pigments, dye molecules have higher solubility and are often dissolved in the photoresist solvent in molecular form, resulting in no scattering and high transmittance. Based on this, Japanese and Korean companies, such as LG Electronics of South Korea and Mitsubishi Corporation of Japan, have gradually developed new color photoresist pastes containing dyes.

[0004] Xanthene dyes are a class of dyes with a dibenzopyran or xanthene structure, primarily including fluorescein and rhodamine. Fluorescein was first synthesized by von Baeyer in 1871, while rhodamine B was first successfully synthesized by Noelting and Dziewonski in 1905.

[0005] Xanthene dyes often have strong fluorescence, covering a wide spectral range from yellow to blue and red, and have excellent photophysical properties, such as high molar extinction coefficient, high fluorescence quantum yield, high stability, easy synthesis and easy modification. Therefore, they can be used in colored photoresist pastes to improve related performance. For example, the blue photoresist developed by Sumitomo Corporation of Japan contains xanthene dyes.

[0006] Currently, the following synthetic method is often used to prepare such rhodamine xanthene dye compounds, and the route is as follows:

[0007] ;

[0008] The first step of this synthetic route is the chlorination of sulfonylfluorescein 1. Different reports have used different chlorination reagents and specific reaction conditions. Subsequently, under different reaction conditions, an amination reaction is carried out on chlorinated sulfonylfluorescein 3 to obtain the target xanthene dye 2.

[0009] Although there are many reports on the preparation methods of the target xanthene dye 2, the current manufacturing methods have the following problems:

[0010] (1) Sulfonyl fluorescein chloride 3 is a key intermediate in the preparation of the final aminated product. Previous manufacturing methods often used chlorination reagents such as thionyl chloride, phosphorus oxychloride, and phosphorus pentachloride to chlorinate sulfonyl fluorescein 1. The chlorination reagents used in this step are all highly acidic and corrosive, and have high requirements for equipment.

[0011] (2) The yield of the above-mentioned chlorination reaction is low (about 30%), and the by-product of the chlorination reaction is hydrochloric acid gas. The post-processing process is complicated, environmentally unfriendly, and the production cost is high;

[0012] (3) The amination reaction of chlorosulfonyl fluorescein 3 requires relatively harsh conditions, such as a high temperature of about 150°C and a large excess of amine (10 times the equivalent), which greatly increases the production cost and the difficulty of post-processing.

[0013] From the above analysis, it can be seen that the current methods for preparing the target xanthene dyes all have corresponding problems and are therefore in urgent need of improvement. Summary of the Invention

[0014] The technical problem to be solved by the present invention is to overcome the technical deficiencies of the background art and provide a method for synthesizing a xanthene dye. The present invention provides a more efficient and cost-effective method for preparing the target xanthene dye. The xanthene dye synthesis method of the present invention avoids the need to first chlorinate sulfonylfluorescein with a strongly acidic and highly corrosive chlorination reagent, such as phosphorus oxychloride, phosphorus pentachloride, or thionyl chloride, as in traditional synthesis methods. This not only reduces the generation of large amounts of strongly acidic gases but also reduces corrosion to production equipment. Furthermore, the nickel-catalyzed CN coupling reaction has mild reaction conditions, significantly reducing the reaction temperature and energy consumption, making this synthesis method more suitable for large-scale industrial production.

[0015] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0016] A method for synthesizing a xanthene dye comprises the following steps:

[0017] (1) In the presence of a base and a catalyst, an esterification reagent is used to esterify the hydroxyl group on sulfonylfluorescein to obtain intermediate A;

[0018] (2) In the presence of a base and a nickel catalyst, the intermediate A undergoes a CN bond coupling reaction with an amine compound to obtain the target xanthene dye 2, which is then applied to a color photoresist;

[0019] The intermediate A is a sulfamate intermediate, a carbamate intermediate or a carboxylate intermediate;

[0020] The chemical structural formulas of the intermediate A and the target xanthene dye 2 are as follows:

[0021] ;

[0022] The above-mentioned synthetic route is as follows:

[0023] ;

[0024] The symbols in the formula have the following meanings:

[0025] R 1 : sulfamate, carbamate or tert-butylcarbonyl;

[0026] R 2 : each independently represents a hydrogen atom, an alkyl substituent (such as a linear, branched, or cyclic alkyl substituent having 1 to 20 carbon atoms), or an aryl substituent (such as a benzene ring, a naphthalene ring, a pyridine ring, an indene ring, an azulene ring, or a heptalene ring);

[0027] R 3 : each independently represents a hydrogen atom, an alkyl substituent (such as a linear, branched, or cyclic alkyl substituent having 1 to 20 carbon atoms), or an aryl substituent (such as a benzene ring, a naphthalene ring, a pyridine ring, an indene ring, an azulene ring, or a heptalene ring);

[0028] R 4 : each independently represents a hydrogen atom, an alkyl substituent (such as a linear, branched, or cyclic alkyl substituent having 1 to 20 carbon atoms), or an aryl substituent (such as a benzene ring, a naphthalene ring, a pyridine ring, an indene ring, an azulene ring, or a heptalene ring);

[0029] R 5 : each independently represents a hydrogen atom, an alkyl substituent (such as a linear, branched, or cyclic alkyl substituent having 1 to 20 carbon atoms), or an aryl substituent (such as a benzene ring, a naphthalene ring, a pyridine ring, an indene ring, an azulene ring, a heptalene ring, or the like).

[0030] Preferably, in step (1), the base is an inorganic base or an organic base, more preferably any one or more of potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, pyridine, triethylamine, 1,8-diazobispiro[5.4.0]undec-7-ene, and N,N-diisopropylethylamine, more preferably any one or more of pyridine, triethylamine, 1,8-diazobispiro[5.4.0]undec-7-ene, and N,N-diisopropylethylamine.

[0031] Preferably, in step (1), the amount of the base used is 1.0 to 2.5 times the equivalent, more preferably 1.1 to 1.5 times the equivalent.

[0032] Preferably, in step (1), the catalyst is any one or more of N,N-diisopropylethylamine, 4-dimethylaminopyridine DMAP, and triethylamine, more preferably any one or two of 4-dimethylaminopyridine DMAP and triethylamine.

[0033] Preferably, in step (1), the amount of the catalyst used is 0.01 to 0.2 equivalents, more preferably 0.05 to 0.15 equivalents.

[0034] Preferably, in step (1), the esterification reagent is any one of pivalic anhydride, pivaloyl chloride, aminosulfonyl chloride, dimethylaminosulfonyl chloride, and N,N-diethylchloroformamide, more preferably any one of pivalic anhydride, pivaloyl chloride, and aminosulfonyl chloride.

[0035] Preferably, in step (1), the amount of the esterification reagent used is 1.0 to 2.5 equivalents, more preferably 1.05 to 1.2 equivalents.

[0036] Preferably, in step (1), the solvent used in the esterification reaction is any one or more of toluene, tetrahydrofuran, benzene, dichloromethane (DCM), dichloroethane, chloroform, 1,4-dioxane, and xylene, and more preferably any one or more of tetrahydrofuran, dichloromethane (DCM), dichloroethane, chloroform, and 1,4-dioxane.

[0037] Preferably, in step (1), the temperature of the esterification reaction does not exceed 30°C, more preferably 0-25°C.

[0038] Preferably, in step (1), the intermediate A is subjected to post-treatment, and the post-treatment includes any one or more of extraction, flash chromatography, and crystallization.

[0039] Preferably, in step (2), the base is an inorganic base or an organic base, more preferably any one or more of potassium tert-butoxide, sodium tert-butoxide, lithium tert-butoxide, n-butyl lithium, potassium carbonate, sodium carbonate, sodium hydroxide, potassium hydroxide, pyridine, triethylamine, 1,8-diazobispiro[5.4.0]undec-7-ene, N,N-diisopropylethylamine, more preferably any one or more of potassium tert-butoxide, sodium tert-butoxide, and lithium tert-butoxide.

[0040] Preferably, in step (2), the amount of the base used is 1.0 to 2.0 times the equivalent, more preferably 1.05 to 1.3 times the equivalent.

[0041] Preferably, in step (2), the nickel catalyst is any one or more of bis-(1,5-cyclooctadiene) nickel, nickel acetylacetonate, nickel chloride dimethoxyethane, nickel chloride, and nickel bromide, more preferably any one or more of bis-(1,5-cyclooctadiene) nickel, nickel acetylacetonate, and nickel chloride dimethoxyethane.

[0042] Preferably, in step (2), the nickel catalyst is used in an amount of 0.01 to 0.2 equivalents, more preferably 0.02 to 0.1 equivalents.

[0043] Preferably, in step (2), the ligand of the nickel catalyst is any one or more of 1,2-bis(diphenylphosphino)ethane, 1,1'-bis(diphenylphosphino)ferrocene, 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride, 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride, bipyridine, and phenanthroline, more preferably 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride or 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride.

[0044] Preferably, in step (2), the amount of the ligand of the nickel catalyst used is 0.02 to 0.4 times the equivalent, more preferably 0.04 to 0.2 times the equivalent.

[0045] Preferably, in step (2), the amine compound is at least one of the following structures: a primary amine or a secondary amine, the general structure of which is NR 6 R 7 R 8 , where R 6 、R 7 R is independently selected from hydrogen, alkyl with 1 to 6 carbon atoms, cycloalkyl with 3 to 8 carbon atoms, aryl or heteroaryl. 8 It is hydrogen or an alkyl group with 1 to 6 carbon atoms; aromatic amine, whose general structural formula is Ar-NHR 9 , wherein Ar is phenyl, naphthyl or heteroaryl containing 1 to 3 heteroatoms (selected from N, O, S), and Ar is optionally substituted by an alkyl group having 1 to 4 carbon atoms, a halogen group, a nitro group or a cyano group, and R 9 The amine compound is selected from hydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms, an aryl group or a heteroaryl group. The amine compound is more preferably diethylamine or N-ethylaniline.

[0046] Preferably, in step (2), the amount of the amine compound used is 2.0 to 5.0 times the equivalent, more preferably 2.0 to 3.0 times the equivalent.

[0047] Preferably, in step (2), the solvent used in the CN bond coupling reaction is any one or more of toluene, tetrahydrofuran, benzene, dichloromethane (DCM), dichloroethane, chloroform, 1,4-dioxane, and xylene, more preferably any one or more of toluene, tetrahydrofuran, 1,4-dioxane, and xylene.

[0048] Preferably, in step (2), the temperature of the CN bond coupling reaction is room temperature to 150°C, more preferably 60 to 120°C.

[0049] Preferably, in step (2), the xanthene dye 2 is post-treated, and the post-treatment includes column chromatography.

[0050] The present invention relates to a novel synthetic method for preparing xanthene dyes. First, the hydroxyl group on sulfonylfluorescein is subjected to an esterification reaction to obtain an intermediate A, wherein the intermediate A is a sulfamate intermediate, a carbamate intermediate, or a carboxylate intermediate. Subsequently, under nickel catalysis, the intermediate A is subjected to a C-N bond coupling reaction with an amine compound to construct a target xanthene dye.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The present invention avoids the use of highly acidic and corrosive chlorination reagents such as phosphorus oxychloride and phosphorus pentachloride required by traditional methods, thereby reducing corrosion to production equipment. This method has simple post-processing and high safety, greatly reducing production costs and improving the feasibility of large-scale production.

[0053] (2) The nickel-catalyzed CN coupling method used in the present invention reduces the reaction temperature, reduces the amount of amine used, and uses less catalyst, simplifies post-processing, and reduces production costs;

[0054] (3) The present invention can be widely used in the preparation of various types of amine-substituted xanthracene dyes, and has excellent substrate applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 The compound 2A prepared in Example 3 of the present invention 1 H-NMR spectrum;

[0056] Figure 2 The compound 2A prepared in Example 3 of the present invention 13 C-NMR spectrum;

[0057] Figure 3 The compound 2B prepared in Example 4 of the present invention 1 H-NMR spectrum;

[0058] Figure 4The compound 2B prepared in Example 4 of the present invention 13 C-NMR spectrum. DETAILED DESCRIPTION

[0059] In order to better understand the content of the present invention, the following is further described in conjunction with specific examples and accompanying drawings. It should be understood that these embodiments are only used to further illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content described in the present invention, those skilled in the art may make some non-essential changes or adjustments to the present invention, which still fall within the scope of protection of the present invention.

[0060] The present invention utilizes LC-MS to determine the structure of the compound and uses the integrated area in LC-MS to obtain the purity of the compound.

[0061] Example 1 (Synthesis of Intermediate A1-1)

[0062] Method 1: To a clean 500 mL three-necked flask, place a stirrer of appropriate size. Add sulfonylfluorescein (37.05 g, 100.9 mmol, 1.0 eq.) and DMAP (12 mg), followed by dissolution with pyridine (200 mL). The mixture was stirred in an ice-water bath for 15 minutes. After the temperature of the mixture stabilized at 0°C, pivaloyl chloride (25.55 g, 211.9 mmol, 2.1 eq.) was added dropwise. After the addition of pivaloyl chloride was complete, the reaction mixture was brought to room temperature and allowed to react overnight. The next day, the reaction was quenched by adding deionized water, followed by multiple extractions with 100 mL of dichloromethane (DCM). The organic phase was dried over anhydrous sodium sulfate, filtered, and the solvent removed by vacuum distillation to obtain 61.53 g of the crude intermediate A1-1 (88% yield). The crude intermediate A1-1 was directly processed without purification.

[0063] Method 2: In a clean 500 mL three-necked flask, place a stirrer of appropriate size; suspend sulfonylfluorescein (18.47 g, 50.1 mmol, 1.0 eq.) in anhydrous toluene (250 mL), then add pivaloyl chloride (12.4 g, 102.8 mmol, 2.1 eq.), triethylamine (15.3 mL, 110.2 mmol, 2.2 eq.), and DMAP (5 mg); stir the reaction mixture under nitrogen at room temperature for 24 h; filter the solid and wash it with toluene; remove the solvent under reduced pressure, and purify the residue twice by flash chromatography (petroleum ether:ethyl acetate = 5:1) or crystallization to obtain 21.78 g of the purified product, intermediate A1-1, with a yield of 81%, which is then used for the next reaction.

[0064] Method 3: Take a clean 500 mL three-necked flask and place a stirrer of appropriate size; suspend sulfonylfluorescein (18.47 g, 50.1 mmol, 1.0 eq.) in anhydrous toluene (250 mL), then add pivalic anhydride (16.7 g, 102.8 mmol, 2.1 eq.), triethylamine (15.3 mL, 110.2 mmol, 2.2 eq.), and DMAP (5 mg); stir the reaction mixture under nitrogen at room temperature for 24 hours; filter the solid and wash it with toluene; remove the solvent under reduced pressure, and purify the residue twice by flash chromatography (petroleum ether:ethyl acetate = 5:1) or crystallization to obtain 20.4 g of the purified product intermediate A1-1 with a yield of 76%, which is then carried out to the next step.

[0065] The chemical structural formula of the intermediate A1-1 is as follows:

[0066] .

[0067] Example 2 (Synthesis of Intermediate A1-2)

[0068] In a clean 500 mL three-necked flask, place a stirrer of appropriate size. Dissolve sulfonylfluorescein (18.47 g, 50.1 mmol, 1.0 eq.) and DMAP (12 mg) in 200 mL of anhydrous pyridine and stir in an ice-water bath for 15 minutes. After the temperature of the system stabilizes at 0°C, add aminosulfonyl chloride (11.88 g, 102.8 mmol, 2.1 eq.) dropwise. After the addition of aminosulfonyl chloride is complete, bring the reaction system to room temperature and allow it to react overnight. The next day, quench the reaction by adding deionized water, followed by multiple extractions with 100 mL of dichloromethane (DCM). Dry the organic phase with anhydrous sodium sulfate, filter, and remove the solvent by vacuum distillation to obtain 20.31 g of the crude intermediate A1-2 in a 77% yield. The crude intermediate A1-2 can be directly processed without purification.

[0069] The chemical structural formula of the intermediate A1-2 is as follows:

[0070] .

[0071] Example 3 (Synthesis of Compound 2A)

[0072] Catalyst bis-(1,5-cyclooctadiene) nickel (350 mg, 1.25 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (1.05 g, 2.5 mmol), sodium tert-butoxide (6.73 g, 70 mmol), A1-1 prepared by method 2 in Example 1 (26.8 g, 50 mmol), N-ethylaniline (14.54 g, 120 mmol) and toluene (250 mL) were placed under a nitrogen atmosphere; the reaction mixture was stirred at 70°C for 3 hours; after cooling to room temperature, the crude mixture was purified by silica gel flash column chromatography (eluent: methanol / dichloromethane = 1:10) to obtain compound 2A as a purple-red solid powder (26.44 g, 92%).

[0073] The chemical structural formula of the compound 2A is as follows:

[0074] .

[0075] The compound 2A 1 H-NMR spectrum and 13 C-NMR spectra are shown in Figure 1 and Figure 2 .

[0076] Example 4 (Synthesis of Compound 2B)

[0077] Catalyst bis-(1,5-cyclooctadiene) nickel (350 mg, 1.25 mmol), 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride (1.05 g, 2.5 mmol), sodium tert-butoxide (6.73 g, 70 mmol), A1-1 prepared by method 2 in Example 1 (26.8 g, 50 mmol), diethylamine (8.78 g, 120 mmol) and toluene (250 mL) were placed under a nitrogen atmosphere; the reaction mixture was stirred at 70°C for 3 hours; after cooling to room temperature, the crude mixture was purified by silica gel flash column chromatography (eluent: methanol / dichloromethane = 1:10) to obtain compound 2B as a purple-red solid powder (21.51 g, 90%).

[0078] The chemical structural formula of the compound 2B is as follows:

[0079] .

[0080] The compound 2B 1 H-NMR spectrum and 13 C-NMR spectra are shown in Figure 3 and Figure 4 .

[0081] Comparative Example 1 (Synthesis of Compound 2A)

[0082] (1) Synthesis of chlorinated intermediate A2

[0083] To a clean 250 mL single-necked flask, place a stirrer of appropriate size. Add sulfonylfluorescein (18.47 g, 50.1 mmol, 1.0 eq.) and phosphorus oxychloride (76.67 g, 0.5 mol, 1.0 eq.), respectively. Heat the mixture to 105°C and stir at 105°C for 18 hours. After the reaction, cool to room temperature. Then, add the resulting reaction solution dropwise to a 2 L three-necked flask containing 1 L of water in an ice-water bath at below 20°C. After addition, stir at 20°C for 1 hour. The resulting suspension is filtered and rinsed once with 200 mL of water and twice with 200 mL of acetonitrile. The rinsed product is air-dried at 50°C for 12 hours to obtain 6.7 g of chlorinated intermediate A2 (33% yield), which is then used for the next reaction.

[0084] The chemical structural formula of the chlorinated intermediate A2 is as follows:

[0085] .

[0086] (2) Synthesis of compound 2A

[0087] To a clean 250 mL single-necked flask, place a stirrer of appropriate size. Compound A2 (4.06 g, 10 mmol, 1.0 eq.), N-ethylaniline (12.12 g, 100 mmol, 10 eq.), and N-methylpyrrolidone (50 mL) were added separately under light-shielding conditions. The reaction mixture was stirred at 125°C and reacted overnight. After cooling to room temperature, the crude mixture was purified by silica gel flash column chromatography (eluent: methanol / dichloromethane = 1:20) to obtain compound 2A as a purple-red solid powder (1.7 g, 29.6%).

[0088] The chemical structural formula of the compound 2A is as follows:

[0089] .

[0090] The synthesis method of the xanthene dye of the present invention avoids the need to first chlorinate sulfonylfluorescein with a strongly acidic and highly corrosive chlorination reagent, such as phosphorus oxychloride, phosphorus pentachloride, or thionyl chloride, as in traditional synthesis methods. This not only reduces the generation of a large amount of strongly acidic gas, but also reduces corrosion to production equipment. In addition, the nickel-catalyzed CN coupling reaction has mild conditions, greatly reduces the reaction temperature, and reduces energy consumption, making this synthesis method more suitable for large-scale industrial production.

[0091] The above description is not intended to limit the present invention, and the present invention is not limited to the above examples. Any changes, modifications, additions or substitutions made by persons of ordinary skill in the art within the spirit and scope of the present invention shall also fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing a xanthene dye, characterized in that: The steps include: (1) In the presence of a base and a catalyst, an esterification reagent is used to esterify the hydroxyl group on sulfonylfluorescein to obtain intermediate A; (2) In the presence of a base and a nickel catalyst, the intermediate A undergoes a CN bond coupling reaction with an amine compound to obtain the target xanthene dye 2; In step (2), the base is an organic base; In step (2), the nickel catalyst is any one or both of bis-(1,5-cyclooctadiene) nickel and nickel acetylacetonate; the ligand of the nickel catalyst is any one or both of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride; The intermediate A is a sulfamate intermediate, a carbamate intermediate or a carboxylate intermediate; The chemical structural formulas of the intermediate A and the target xanthene dye 2 are as follows: The symbols in the formula have the following meanings: R 1 : aminosulfonyl, carbamoyl or tert-butylcarbonyl; R 2 : each independently represents a hydrogen atom, an alkyl group, or an aryl group; R 3 : each independently represents a hydrogen atom, an alkyl group, or an aryl group; R 4 : each independently represents a hydrogen atom, an alkyl group, or an aryl group; R 5 : Each independently represents a hydrogen atom, an alkyl group, or an aryl group.

2. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (1), the base is an inorganic base or an organic base.

3. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (1), the catalyst is any one or more of N,N-diisopropylethylamine, 4-dimethylaminopyridine, and triethylamine.

4. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (1), the esterification reagent is any one of pivalic anhydride, pivaloyl chloride, and aminosulfonyl chloride.

5. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (1), the amount of the base used is 1.0 to 2.5 times the equivalent; the amount of the catalyst used is 0.01 to 0.2 times the equivalent; and the amount of the esterification agent used is 1.0 to 2.5 times the equivalent.

6. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (1), the temperature of the esterification reaction does not exceed 30°C.

7. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (2), the amount of the base is 1.0 to 2.0 times the equivalent; the amount of the nickel catalyst is 0.01 to 0.2 times the equivalent; the amount of the ligand of the nickel catalyst is 0.02 to 0.4 times the equivalent; and the amount of the amine compound is 2.0 to 5.0 times the equivalent.

8. The method for synthesizing a xanthene dye according to claim 1, wherein: In step (2), the temperature of the CN bond coupling reaction is room temperature to 150°C.

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