An olefin-linked cofs, and a method for catalyzing hydroxylation of imidazo[1,2-a]pyridine c3-h bond

Abstract

The application provides an olefin-linked COF and a method for catalyzing hydroxylation of an imidazo[1,2-a]pyridine C3-H bond, and belongs to the technical field of imidazopyridine derivative synthesis, and aims to solve the technical problems of high reaction temperature and use of strong oxidants in the reaction of hydroxylation of an imidazo[1,2-a]pyridine C3-H bond. The application uses the olefin-linked COF as a photocatalyst, uses imidazo[1,2-a]pyridine derivatives with different substitutions as reactants, and directly generates a C3-hydroxylated product in an air or oxygen environment at room temperature, in an organic solvent and water and under light irradiation. The catalytic reaction of the application is carried out at room temperature, only visible light irradiation is needed, heating and strong oxidants are not needed, the catalytic condition requirement is simple, and the catalytic process is energy-saving, environment-friendly and safe. The catalyst has good stability, the catalyst activity does not change obviously after multiple cycles, and has a strong industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the technical field of imidazopyridine derivative synthesis, and particularly relates to an olefin-linked COFs and a method for catalyzing the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine. Background Technology

[0002] Imidazolidine heterocycles have attracted great attention from chemists in organic synthesis research, mainly due to their good biological activity and wide application in medicinal chemistry, such as antitumor, antiviral, antibacterial, and anti-inflammatory effects (Almirante L, Polo L, Mugnaini A, et al. Derivatives of Imidazole. IS synthesis and Reactions of Imidazo[1,2-α]pyridines with Analgesic, Antiinflammatory, Antipyretic, and Anticonvulsant Activity. J. Med. Chem., 1965(8):305). Furthermore, hydroxylation is a very important step in organic synthesis. Hydroxylation reactions can directly introduce hydroxyl groups into organic compound molecules, thereby obtaining alcohols and phenols, which have very wide applications in fine chemicals. Hydroxylation can also increase the hydrophilicity of organic molecules or biologically active heterocycles, and facilitate further functional group reactions. Currently, the functionalization of imidazopyridine heterocycles at the C3 position has been extensively studied, especially the functionalization at the C3 position of the imidazo ring. Research on the C3-H functionalization of imidazopyridine heterocycles mainly focuses on halogenation, alkyl nitrification, sulfidation, and amination, while research on the C3-H hydroxylation of imidazopyridine heterocycles is scarce. In 2020, Sandeep Chaudhary et al. developed a method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridines without transition metal involvement (Yadav RK, Kumar Y, Chaudhary S. Metal-Free, H2O2-Mediated, Regioselective Direct C-3Hydroxylation of I midazo[1,2-a]pyridines via C(sp~2)-H Bond Functionalization. Chemistry Select, 2020(29):5.). However, this method has serious drawbacks such as high reaction temperature and the use of strong oxidants. In particular, since many organic compounds are flammable and explosive, the use of organic compounds and strong oxidants under high temperature conditions increases the danger of the experiment.

[0003] In recent years, visible light photocatalysis has become a highly efficient and practical tool in the chemical field because it allows reactions to occur under mild conditions (usually room temperature). However, previously, chemists did not pay much attention to this field until 2008 when MacMillan et al. applied visible light photocatalysis as an environmentally friendly and powerful tool to organic synthesis. Since then, visible light photocatalysis has become a hot research topic and has received increasing attention. Copolymers (COFs), due to their high absorbance and excellent photoelectric properties, can maintain structural stability in water, organic solvents, and even strong acid and base environments, making them highly efficient photocatalyst materials. Over time, more and more COF materials have been used in various photocatalytic reactions, such as hydrogen evolution from water, carbon dioxide reduction, organic synthesis reactions, and pollutant degradation, and the application of COFs in photocatalysis has made significant progress. Photocatalytic hydroxylation reactions driven by COFs have also made some progress, enabling the preparation of phenolic substances under excellent reaction conditions without heating. However, the reaction systems are all based on the oxidation of arylboronic acids (Wei PF, Qi MZ, Wang ZP, et al. Benzoxazole-Linked Ultrastable Covalent Organic Frameworks for Photocatalysis. J. Am. Chem. Soc., 2018(140):4623). The preparation of arylboronic acids requires the prefunctionalization of aromatic compounds, which increases the number of steps and costs involved in the preparation of phenolic substances. Summary of the Invention

[0004] To address the technical problems of high reaction temperature and the use of strong oxidants in the C3-H hydroxylation reaction of imidazo[1,2-a]pyridine, this invention proposes a method for linking COFs to olefins and catalyzing the C3-H hydroxylation reaction of imidazo[1,2-a]pyridine. The catalytic reaction of this invention is carried out at room temperature, requiring only visible light irradiation, without the need for heating or strong oxidants. It has simple catalytic requirements and the catalytic process is energy-saving, environmentally friendly, and safe. The reaction of this invention is a heterogeneous catalytic reaction, with a catalyst exhibiting good stability and recyclability. The catalyst activity does not significantly change after multiple cycles, demonstrating strong industrial application prospects.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] An olefin-linked COFs photocatalyst is synthesized from terephthalaldehyde and trimethyltriazine with different substituents via a solvothermal method under acidic conditions, as shown in the following reaction formula:

[0007]

[0008] The preparation method based on olefin-linked COFs includes the following steps: terephthalaldehyde with different substituents is mixed with trimethyltriazine monomer and then added to a solvent. After being dispersed evenly by ultrasonic vibration, acid is added and the mixture is heated to react for a period of time. After the reaction is completed, olefin-linked COFs material is obtained.

[0009] The terephthalaldehyde with different substituents, wherein the substituent is one of fluorine, chlorine, or bromine atoms.

[0010] The molar ratio of terephthalaldehyde with different substituents to trimethyltriazine is (1-1.5):(1-1.5).

[0011] The solvent is a mixed solution of mesitylene, 1,4-dioxane and acetonitrile, with a volume ratio of (4-40):(4-40):(1-5).

[0012] The mass-to-volume ratio of the reactants to the solvent is 11.8-30.3 mg / mL; the acid is trifluoroacetic acid, and its amount is 15%-20% of the solvent volume; the reaction temperature is 80-200℃, and the reaction time is 10-100 h; after the reaction, the product is washed sequentially with concentrated ammonia solution, anhydrous methanol, and tetrahydrofuran, and then vacuum dried at 60-100℃ for 6-12 h.

[0013] This method utilizes photocatalytic hydroxylation of imidazo[1,2-a]pyridine C3-H bonds based on olefin-linked COFs. Olefin-linked COFs are used as photocatalysts, and imidazo[1,2-a]pyridine derivatives with different substitutions are used as reactants. The reaction is carried out in an air or oxygen environment at room temperature (usually 20-25 degrees Celsius, room temperature, no heating or cooling required), with organic solvent and water, and under light irradiation for 5-30 hours. After the reaction, the reaction solvent is removed, and the imidazo[1,2-a]pyridine C3-H bond hydroxylated derivatives are obtained by column chromatography or recrystallization.

[0014] The structural formula of the imidazo[1,2-a]pyridine derivatives with different substitutions is as follows: R 1 R 2 It is one or more of aryl, heterocyclic, alkyl, alkoxy, hydroxyl, amino, acetamido, nitro, sulfonyl, nitrile, polyfluoroalkyl, and halogen atoms; the aryl group is one of phenyl, naphthyl, phenanthryl, or pyrene; the heterocyclic group is one of furanyl, thiophene, pyridyl, pyrimidinyl, thiazolyl, or imidazolyl; and the alkyl group is one of methyl, ethyl, propyl, butyl, isopropyl, tert-butyl, or cyclohexyl. 1 R2 They can be the same or different.

[0015] The amount of the olefin-linked COFs photocatalyst used is 0.05-0.5 times the mass of the imidazo[1,2-a]pyridine derivative.

[0016] The organic solvent is one or more of methanol, ethanol, tetrahydrofuran, 1,4-dioxane, o-xylene, N,N-dimethylformamide, dimethyl sulfoxide, petroleum ether, cyclohexane, n-hexane, ethyl acetate, 1,2-dichloroethane, or dichloromethane; the volume ratio of the organic solvent to water is (7-15):1; the mass-volume ratio of the imidazo[1,2-a]pyridine derivative to the sum of the volumes of the solvent is 10-50 mg / mL.

[0017] The illumination is visible light with a wavelength of λ≥420nm.

[0018] After the synthesis reaction is completed in this invention, there are no particular limitations on the post-processing. First, the reaction mixture is filtered, and the filter residue is washed with solvent to obtain the COFs catalyst for reuse. Then, the solvent in the filtrate is removed, and the target product is obtained by column chromatography or recrystallization.

[0019] Taking 2-phenylimidazo[1,2-a]pyridine as an example, the reaction mechanism involved in this invention is shown in the following formula:

[0020]

[0021] The beneficial effects of this invention are:

[0022] (1) The covalent organic framework material preparation method designed in this invention is simple and easy to implement, and can be prepared by common solvothermal methods.

[0023] (2) The covalent organic framework material prepared in this invention exhibits excellent photocatalytic activity in the photocatalytic hydroxylation of imidazo[1,2-a]pyridine C3-H bonds. This is attributed to the extremely high specific surface area (750 m²) of the covalent organic framework material. 2 g –1 This allows for the exposure of more catalytic active centers, enabling them to participate in photocatalytic reactions. Furthermore, olefin-linked COFs materials exhibit full conjugation, which helps improve the mobility of charge carriers, potentially enhancing the catalytic performance of the material.

[0024] (3) As a photocatalytic material, the catalytic reaction is carried out at room temperature. It only requires visible light irradiation and does not require heating or strong oxidants. The catalytic conditions are simple, and the catalytic process is energy-saving, environmentally friendly and safe.

[0025] (4) The reaction of the present invention is a heterogeneous catalytic reaction. The catalyst has good stability and can be recycled multiple times. Moreover, the catalyst activity does not change significantly after multiple cycles. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 XRD pattern of COF-1 linked to olefin;

[0028] Figure 2 BET spectrum for COF-1 linked in olefins;

[0029] Figure 3 UV-vis DRS spectrum of COF-1 linked to olefin;

[0030] Figure 4 Kubelka-Munk transition spectrum for COF-1 linkage in olefins;

[0031] Figure 5 XRD pattern of COF-2 linked to olefin;

[0032] Figure 6 UV-vis DRS spectrum of COF-2 linked to olefin;

[0033] Figure 7 Kubelka-Munk transition spectrum for COF-2 linked to olefins;

[0034] Figure 8 XRD pattern of COF-3 linked to olefin;

[0035] Figure 9 UV-vis DRS spectrum of COF-3 linked to olefin;

[0036] Figure 10 Kubelka-Munk transition spectrum for COF-3 linkage in olefins;

[0037] Figure 11 and 12 The 1H and 1C NMR spectra of hydroxylated product 1 are shown.

[0038] Figure 13 This is a test of the recycling capacity of COF-1. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] The synthesis of olefin-linked COFs-1 involves the following steps: 2,5-Difluoroterephthalaldehyde (0.15 mmol, 25.6 mg), trimethyltriazine (0.10 mmol, 12.3 mg), and a mixed solvent of mesitylene / 1,4-dioxane / acetonitrile (volume ratio 20:20:1) are added to a 10 mL ampoule. After ultrasonically dispersing the mixture, 307.5 μL of trifluoroacetic acid is added. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature to allow the liquid to completely thaw, and then placed in an oven preheated to 120°C for 72 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 100 °C for 6 h, and then brought to room temperature to obtain olefin-linked COFs-1 with a yield of 29.8 mg and a yield of 78.6%.

[0042] XRD and BET tests were performed on the olefin-linked COF-1: the obvious peak at 4.58° in the XRD results proves that the olefin-linked COF-1 has good crystallinity (e.g., Figure 1 The BET test results showed that the specific surface area of ​​the olefin-linked COF-1 was 750 m². 2 g –1 (like Figure 2 This demonstrates that the olefin-linked COF-1 possesses a porous structure. Further analysis using UV-Vis diffuse reflectance spectroscopy (e.g., ...) confirmed this. Figure 3 The light absorption range of this material is approximately 250-700 nm. The UV-vis DRS spectrum of COF-1 was subjected to Kubelka Munk conversion (e.g., ...). Figure 4 It was found that COF-1 is an n-type semiconductor with a band gap of 2.46 eV.

[0043] Example 2

[0044] The synthesis of olefin-linked COFs-1 involves the following steps: 2,5-Difluoroterephthalaldehyde (0.10 mmol, 17.1 mg), trimethyltriazine (0.15 mmol, 18.5 mg), and 2.45 mL of a mixed solvent of mesitylene / 1,4-dioxane / acetonitrile (volume ratio 4:40:5) are added to a 10 mL ampoule. The mixture is ultrasonically dispersed and then heated to 490 μL of trifluoroacetic acid. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature until the liquid completely thaws, and then placed in an oven preheated to 80°C for 100 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 60 °C for 12 h, and then brought to room temperature to obtain olefin-linked COFs-1 with a yield of 18.9 mg and a yield of 53.1%.

[0045] Example 3

[0046] The synthesis of olefin-linked COFs-1 involves the following steps: 2,5-Difluoroterephthalaldehyde (0.15 mmol, 25.6 mg), trimethyltriazine (0.15 mmol, 18.5 mg), and 2.30 mL of a mixed solvent of mesitylene / 1,4-dioxane / acetonitrile (volume ratio 40:4:2) are added to a 10 mL ampoule. The mixture is ultrasonically dispersed and then heated to 414 μL of trifluoroacetic acid. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature to allow the liquid to completely thaw, and then placed in an oven preheated to 200°C for 10 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 80 °C for 8 h, and then brought to room temperature to obtain olefin-linked COFs-1 with a yield of 35.7 mg and a yield of 80.9%.

[0047] Example 4

[0048] The synthesis of olefin-linked COFs-1 involves the following steps: 2,5-Difluoroterephthalaldehyde (0.10 mmol, 17.1 mg), trimethyltriazine (0.10 mmol, 12.3 mg), and 2.50 mL of a mixed solvent of mesitylene / 1,4-dioxane / acetonitrile (volume ratio 40:8:2) are added to a 10 mL ampoule. The mixture is ultrasonically dispersed and then heated to 400 μL of trifluoroacetic acid. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature to allow the liquid to completely thaw, and then placed in an oven preheated to 150°C for 48 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 90 °C for 7 h, and then brought to room temperature to obtain olefin-linked COFs-1 with a yield of 21.2 mg and a yield of 72.1%.

[0049] Example 5

[0050] The synthesis of olefin-linked COFs-2 involves the following steps: 1.85 mL of a mixed solvent of 2,5-dichloroterephthalaldehyde (0.15 mmol, 30.5 mg), trimethyltriazine (0.10 mmol, 12.3 mg), and mesitylene / 1,4-dioxane / acetonitrile (volume ratio 18:18:1) is added to a 10 mL ampoule. The mixture is ultrasonically dispersed and then heated to 370 μL of trifluoroacetic acid. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature to allow the liquid to completely thaw, and then placed in an oven preheated to 120°C for 72 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 100 °C for 6 h, and then brought to room temperature to obtain olefin-linked COFs-2 with a yield of 35.1 mg and a yield of 82.0%.

[0051] like Figure 5 As shown, the olefin-linked COF-2 exhibits good crystallinity as indicated by the distinct peak at 4.74° in the XRD results. Further analysis using UV-Vis diffuse reflectance spectroscopy (e.g., ...) confirms that the olefin-linked COF-2 possesses good crystallinity. Figure 6 The light absorption range of this material is approximately 250-700 nm. The UV-vis DRS spectrum of COF-2 was subjected to Kubelka Munk conversion (e.g., ...). Figure 7 It was found that COF-1 is an n-type semiconductor with a band gap of 2.57 eV.

[0052] Example 6

[0053] The synthesis of olefin-linked COFs-3 involves the following steps: 1.85 mL of a mixed solvent of 2,5-dibromo-terephthalaldehyde (0.15 mmol, 43.8 mg), trimethyltriazine (0.10 mmol, 12.3 mg), and mesitylene / 1,4-dioxane / acetonitrile (volume ratio 36:4:1) is added to a 10 mL ampoule. The mixture is ultrasonically dispersed and then heated to 370 μL of trifluoroacetic acid. The ampoule is then immersed in liquid nitrogen for 5 min, followed by vacuum pumping for 5 min under freezing conditions. The vacuum pumping is then stopped, and the ampoule is placed at room temperature until the liquid thaws. This "freezing-vacuuming-thawing" process is repeated twice. The ampoule is then frozen, and the neck is heated and sealed under vacuum. The sealed ampoule is placed at room temperature to allow the liquid to completely thaw, and then placed in an oven preheated to 150°C for 80 h. After the reaction was completed, the mixture was brought to room temperature, filtered, and then washed with concentrated ammonia (20 mL * 3), methanol (20 mL * 3), and tetrahydrofuran (20 mL * 3), respectively. It was then dried in a vacuum drying oven at 90 °C for 10 h, and then brought to room temperature to obtain olefin-linked COFs-1 with a yield of 46.8 mg and a yield of 83.5%.

[0054] like Figure 8 As shown, the olefin-linked COF-3 exhibits XRD patterns. The distinct peak at 4.97° in the XRD results confirms that the olefin-linked COF-3 possesses a certain degree of crystallinity. Further analysis using UV-Vis diffuse reflectance spectroscopy (e.g., ...) confirms this. Figure 9 The light absorption range of this material is approximately 250-650 nm. The UV-vis DRS spectrum of COF-3 was subjected to Kubelka Munk conversion (e.g., ...). Figure 10 It was found that COF-3 is an n-type semiconductor with a band gap of 2.67 eV.

[0055] Example 7

[0056] A method for the C3-H hydroxylation reaction of imidazo[1,2-a]pyridine, comprising the following steps:

[0057] Weigh 39 mg of 2-phenylimidazo[1,2-a]pyridine, 2.0 mg of olefin-linked COF-1 catalyst, 0.7 mL of tetrahydrofuran, and 0.1 mL of water into a 20 mL reaction tube. Add a stir bar and stir for 30 h at 25 °C under an oxygen atmosphere and white light irradiation (λ≥420 nm). After the reaction is complete, remove the catalyst by filtration, remove the solvent from the filtrate using a rotary evaporator, and then obtain 135.7 g of the hydroxylated product by column chromatography, with a yield of 85%.

[0058]

[0059] NMR data of hydroxylated product 1 (e.g.) Figure 11 and 12 ): 1 H NMR (400MHz, CDCl3) δ8.85 (s, 1H), 8.40 (d, J = 8.4Hz, 1H), 8.24 (d, J = 4.0Hz, 1H), 7.94-7 .92(m,2H),7.78-7.74(m,1H),7.59-7.55(m,1H),7.51-7.48(m,2H),7.08-7.04(m,1H); 13 C NMR (100MHz, CDCl3) δ165.8,151.6,147.9,138.5,134.3,132.2,128.8,127.3,119.9,114.3.

[0060] The olefin-linked COF-1 catalyst removed by filtration after the reaction was washed with tetrahydrofuran (20 mL * 3), dried in a vacuum oven at 100 °C for 6 h, removed and allowed to return to room temperature, and then added back into the reaction. This cycle was repeated 5 times, and no significant decrease in the photocatalytic activity of the catalyst was observed (e.g. Figure 13 ).

[0061] Examples 8-17 and Comparative Examples 1-2

[0062] The imidazo[1,2-a]pyridine C3-hydroxylated derivatives were synthesized using the same method as in Example 7. The various reaction conditions and results are shown in Table 1.

[0063] Table 1. Synthesis of various imidazo[1,2-a]pyridine C3-hydroxylated derivatives under different conditions.

[0064]

[0065]

[0066] As can be seen from the above examples, the preparation method of the present invention has wide substrate applicability and the yield can reach medium or above. The olefin-linked COFs catalyst used in this preparation method has high catalytic activity, high reaction efficiency, stable catalyst structure, and no significant change in catalyst activity after multiple uses.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine, characterized in that, Using olefin-linked COFs as photocatalysts, the reactant imidazo[1,2-a]pyridine derivative and the photocatalyst olefin-linked COFs were dissolved in a mixed solvent and reacted under light and oxygen conditions to prepare imidazo[1,2-a]pyridine C3-H bond hydroxylated derivatives. The structure of the olefin-linked COFs is shown in the following formula: In the formula, R is F, Cl, or Br; The structural formula of the imidazo[1,2-a]pyridine derivative is as follows: R 1 R 2 It is one or more of aryl, heterocyclic, alkyl, alkoxy, hydroxyl, amino, acetamido, nitro, sulfonyl, nitrile, polyfluoroalkyl, and halogen atoms; the aryl group is one of phenyl, naphthyl, phenanthryl, or pyrene; the heterocyclic group is one of furanyl, thiophene, pyridyl, pyrimidinyl, thiazolyl, or imidazolyl; and the alkyl group is one of methyl, ethyl, propyl, butyl, isopropyl, tert-butyl, or cyclohexyl. 1 and R 2 Same or different.

2. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 1, characterized in that, The preparation method of the olefin-linked COFs includes the following steps: mixing terephthalaldehyde and trimethyltriazine monomers with different substituents with a solvent, dispersing them evenly, adding acid, heating the reaction, and obtaining olefin-linked COFs after the reaction is completed; the reaction formula is as follows: In the formula, R is F, Cl, or Br.

3. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 2, characterized in that, The molar ratio of terephthalaldehyde with different substituents to trimethyltriazine is (1-1.5):(1-1.5).

4. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 3, characterized in that, The solvent is a mixed solution of mesitylene, 1,4-dioxane and acetonitrile, with a volume ratio of (4-40):(4-40):(1-5).

5. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 4, characterized in that, The total amount of reactants to solvent is 11.8-30.3 mg / mL; the acid is trifluoroacetic acid, and its amount is 15%-20% of the solvent volume; the reaction temperature of the heating reaction is 80-200 °C, and the reaction time is 10-100 h.

6. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 1, characterized in that, The amount of the olefin-linked COFs photocatalyst used is 0.05-0.5 times the mass of the imidazo[1,2-a]pyridine derivative.

7. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 1, characterized in that, The mixed solvent comprises an organic solvent and water, wherein the organic solvent is one or more of methanol, ethanol, tetrahydrofuran, 1,4-dioxane, o-xylene, N,N-dimethylformamide, dimethyl sulfoxide, petroleum ether, cyclohexane, n-hexane, ethyl acetate, 1,2-dichloroethane, or dichloromethane; the volume ratio of the organic solvent to water is (7-15):1; and the mass-volume ratio of the imidazo[1,2-a]pyridine derivative to the mixed solvent is 10-50 mg / mL.

8. The method for the C3-H bond hydroxylation reaction of imidazo[1,2-a]pyridine according to claim 1, characterized in that, The reaction atmosphere is air or oxygen, the reaction temperature is room temperature, the reaction time is 5-30 hours, and the light is visible light with a wavelength λ≥420 nm.

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