Method for synthesizing N-alkyl substituted 3, 5-dimethyl pyrazole compound by one-pot method

Abstract

The invention belongs to the technical field of synthesis of organic compounds, and particularly relates to a method for synthesizing an N-alkyl substituted 3, 5-dimethyl pyrazole compound by a one-pot method. The method comprises the following steps of: 1, adding a cerium catalyst and an organic solvent into alkyl methanol and di-tert-butyl azodicarboxylate serving as raw materials, uniformly stirring, and reacting for a certain time under the illumination condition to obtain a precursor of N-alkyl substituted 3, 5-dimethylpyrazole; spin-drying the reaction system obtained in the first step, and adding a hydrochloric acid methanol solution for reaction; and 3, spin-drying the reaction system obtained in the step 2, and adding acetylacetone, triethylamine and methanol for reaction to obtain the N-alkyl substituted 3, 5-dimethyl pyrazole compound. According to the method, raw materials are easy to obtain, reaction conditions are mild and safe, the cerium catalyst is easy to synthesize and prepare on a large scale, and the method is suitable for green synthesis of the N-alkyl substituted 3, 5-dimethylpyrazole compound.

Description

Technical Field

[0001] The invention belongs to the technical field of organic compound synthesis, and specifically relates to a one-pot method for synthesizing N-alkyl substituted 3,5-dimethylpyrazole compounds. Background Art

[0002] Nitrogen-containing heterocyclic organic compounds occupy an indispensable and important position in the field of pesticide and biomedicine research, and therefore have attracted the attention of many scientists. Pyrazoles are aromatic five-membered nitrogen-containing heterocyclic compounds, and 3,5-dimethylpyrazole is one of the simplest pyrazole compounds. This substance can be used as a pharmaceutical chemical intermediate and a basic raw material for chemical production. It can also be used to prepare new organic semiconductor materials, optoelectronic materials, etc. Therefore, the preparation of 3,5-dimethylpyrazole derivatives occupies an important research position in synthesis.

[0003] The traditional method for preparing 3,5-dimethylpyrazole derivatives is mainly to use hydrazine hydrochloride and acetylacetone as raw materials to prepare the target product through Knorr condensation reaction. In the Knorr condensation reaction, hydrazine hydrochloride and acetylacetone may generate other by-products, such as monoalkylation or dialkylation products, which affect the purity and yield of the target product. In addition, the reaction usually requires high temperature and long time, which increases energy consumption and operation difficulty, and may cause decomposition of raw materials or products. In addition, due to the limited source of hydrazine compounds, the diversity of derivatives is limited; the mixture after the reaction is complex, and the separation and purification steps of the target product are cumbersome, and multiple recrystallization or column chromatography may be required, which increases cost and time.

[0004] Therefore, the traditional method for preparing 3,5-dimethylpyrazole derivatives has certain limitations, and we still need to study it in order to find new methods to overcome the above problems. Summary of the invention

[0005] The object of the present invention is to overcome the deficiencies in the prior art and provide a one-pot method for preparing N-alkyl-substituted 3,5-dimethylpyrazole compounds. The method uses common visible light as a light source, and a stable and easy-to-prepare cerium sodium triisopropylbenzoate complex as a catalyst to achieve dehydroxymethylation and hydrazine reaction of primary alcohols; combined with Boc deprotection and Knorr heterocyclic condensation reaction, the N-alkyl-substituted 3,5-dimethylpyrazole compounds are finally efficiently synthesized through a one-pot three-step reaction. The method has warm reaction conditions, the alcohol raw material is easily available, and the cerium catalyst is stable, and gram-scale preparation can be carried out. Only one-step separation and purification is required to effectively achieve the derivatization of N-alkyl-substituted 3,5-dimethylpyrazole compounds, which provides a certain reference value for the preparation of nitrogen-containing heterocyclic organic compounds.

[0006] In order to achieve the above invention object, the specific technical solution of the present invention is:

[0007] A one-pot method for synthesizing N-alkyl substituted 3,5-dimethylpyrazole compounds, the reaction formula of which is as follows:

[0008]

[0009] Furthermore, the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds described above comprises the following steps:

[0010] The first step: dehydroxymethylation, using alkyl methanol and di-tert-butyl azodicarboxylate (DBAD) as raw materials, adding cerium catalyst and organic solvent, stirring evenly, reacting for a certain time under light conditions, to obtain the precursor of N-alkyl substituted 3,5-dimethylpyrazole;

[0011] Step 2: Boc deprotection, spin dry the reaction system obtained in the first step, add hydrochloric acid methanol solution to react;

[0012] Step 3: Knorr heterocyclic condensation, the reaction system obtained in the second step is dried by rotation, acetylacetone, triethylamine and methanol are added to react to obtain N-alkyl substituted 3,5-dimethylpyrazole compounds.

[0013] Furthermore, in the first step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the organic solvent of the reaction is any one of acetonitrile, benzonitrile (BnCN), chlorobenzene, trifluorotoluene, N,N-dimethylformamide (DMF), acetone and dichloromethane; more preferably acetonitrile.

[0014] Furthermore, in the first step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the cerium catalyst is sodium cerium (IV) pentatriisopropylbenzoate complex (Ce(TRIPCO2)5Na).

[0015] Further, in the first step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the alkylmethanol includes but is not limited to cyclohexylmethanol, cycloheptylmethanol, 1-(methylcyclohexyl)methanol, 3-cyclohexene-1-methanol, bicyclo[2.2.1]hept-2-ylmethanol, 3-hydroxy-1-adamantanemethanol, phenylethanol, 4-bromophenylethanol, 4-(2-hydroxyethyl)benzoic acid methyl ester, 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)ethanol, 2-(benzofuran-5-yl)ethanol, 2-(benzo[b]thiophen-3-yl)ethanol, etc.; the structural formulas are as follows:

[0016]

[0017] Further, in the first step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the molar ratio of alkyl carbinol to di-tert-butyl azodicarboxylate is 1:1.0-5.0, such as 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:5, more preferably 1:1.5 or 1:5; the molar ratio of alkyl carbinol to cerium catalyst is 1:0.01-0.06, such as 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, more preferably 1:0.06. The ratio of the amount of alkyl carbinol (mmol) to the volume (ml) of the organic solvent is 1:5.0-25.0. For example, the specific ratio may be 1:5.0, 1:10.0, 1:15.0, 1:20.0, 1:25.0, and more preferably 1:10.0.

[0018] Furthermore, in the first step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the light source in the first step illumination condition is visible light, more preferably 400nm LEDs, and the light power is 2.5W; the reaction time under the illumination condition is 6-24 hours, specifically 6h, 10h, 14h, 18h, 24h, etc., more preferably 18h or 24h.

[0019] Furthermore, in the second step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the concentration of the methanol hydrochloric acid solution is 4 mol / L, and its amount is 40 times the equivalent of alkyl methanol; the reaction temperature is 40° C., and the reaction time is 3 hours.

[0020] Furthermore, in the third step of the one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, the amount of acetylacetone used is 3 times the equivalent of alkyl methanol; the amount of triethylamine used is 1 times the equivalent of alkyl methanol; the reaction temperature is 40° C., and the reaction time is 3 hours.

[0021] Preferably, the above-mentioned one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds further comprises a fourth step, namely, a separation and purification step.

[0022] Preferably, the specific operation of the separation and purification step is: after the reaction in the third step is completed, the mixture is extracted once with water and ethyl acetate respectively; the organic phases are combined, dried with anhydrous Na2SO4, and further distilled off the solvent under reduced pressure to obtain a crude product; the crude product is then separated by column chromatography to obtain N-alkyl substituted 3,5-dimethylpyrazole compounds.

[0023] The present invention protects N-alkyl substituted 3,5-dimethylpyrazole compounds prepared by the above method, which have high purity.

[0024] Further, the preparation method of the cerium sodium triisopropylbenzoate complex [Ce(TRIPCO2)5Na] is as follows: cerium ammonium nitrate CAN (2.74g, 5mmol), 2,4,6-triisopropylbenzoic acid TRIPCO2H (12.42g, 50mmol) and sodium phosphate (8.20g, 50mmol) are evenly divided into 10 40mL vials under N2 atmosphere to obtain better stirring and heat transfer efficiency, and 20mL acetonitrile is added to each vial. Then, it is heated at 50°C for 3 hours and the filtrate is filtered. The filtrate is volatilized in a glove box filled with nitrogen, and the formed Ce(TRIPCO2)5Na is combined to obtain brown-red crystals (4.36g, total yield is 62%).

[0025] The sodium cerium pentyl triisopropylbenzoate complex catalyst used under light conditions in the present invention is used in the preparation of N-alkyl-substituted 3,5-dimethylpyrazole compounds, and has a high yield, which can reach up to 82% after the three-step reaction is completed.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (i) The present invention uses alcohol, which is easily available as a raw material, and the reaction conditions are mild. Only light is required to achieve the dehydroxymethylation and hydrazine reaction of the alcohol, thereby broadening the source of hydrazine derivatives.

[0028] (ii) The present invention uses air-stable Ce(TRIPCO2)5Na as a photocatalyst and can be prepared on a large scale. The catalyst metal raw material is rare earth metal cerium, which can achieve effective utilization of rare earth metal elements.

[0029] (III) The present invention adopts a one-pot reaction and only requires one separation and purification, and is simple to operate, and is suitable for the rapid synthesis of N-alkyl substituted 3,5-dimethylpyrazole compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is the single crystal diffraction pattern of the cerium catalyst [Ce(TRCPCO2)5Na].

[0031] Figure 2 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-cyclohexyl-3,5-dimethyl-1H-pyrazole prepared in Example 2.

[0032] Figure 3 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-cycloheptyl-3,5-dimethyl-1H-pyrazole prepared in Example 3.

[0033] Figure 4These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-methylcyclohexyl-3,5-dimethyl-1H-pyrazole prepared in Example 4.

[0034] Figure 5 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-(3-cyclohexenyl)-3,5-dimethyl-1H-pyrazole prepared in Example 5.

[0035] Figure 6 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-bicyclo[2.2.1]hept-2-yl-3,5-dimethyl-1H-pyrazole prepared in Example 6.

[0036] Figure 7 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 3-(3,5-dimethyl-1H-pyrazol-1-yl)-adamantan-1-ol prepared in Example 7.

[0037] Figure 8 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-benzyl-3,5-dimethyl-1H-pyrazole prepared in Example 8.

[0038] Fig. 9 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-(4-bromobenzyl)-3,5-dimethyl-1H-pyrazole prepared in Example 9.

[0039] Fig.10 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzoic acid methyl ester prepared in Example 10.

[0040] Fig.11 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)-1H-pyrazole prepared in Example 11.

[0041] Fig.12 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-(benzofuran-5-ylmethyl)-3,5-dimethyl-1H-pyrazole prepared in Example 12.

[0042] Fig.13 These are the hydrogen nuclear magnetic resonance spectrum and carbon nuclear magnetic resonance spectrum of the compound 1-(benzo[b]thiophen-3-ylmethyl)-3,5-dimethyl-1H-pyrazole prepared in Example 13. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes and modifications to the present invention, but these equivalent forms also fall within the scope defined by the claims attached to the application.

[0044] The one-pot method for synthesizing N-alkyl substituted 3,5-dimethylpyrazole compounds of the present invention is described in detail below in combination with the specific principles and preparation process.

[0045] The preparation method of the cerium sodium pentyl triisopropylbenzoate complex [Ce(TRIPCO2)5Na] used in the following examples is as follows:

[0046] Cerium ammonium nitrate CAN (2.74 g, 5 mmol), 2,4,6-triisopropylbenzoic acid TRIPCO2H (12.42 g, 50 mmol) and sodium phosphate (8.20 g, 50 mmol) were evenly divided into 10 40 mL vials under N2 atmosphere to obtain better stirring and heat transfer efficiency, and 20 mL of acetonitrile was added to each vial. Then heated at 50 ° C for 3 hours and filtered to obtain the filtrate. The filtrate was evaporated in a glove box filled with nitrogen, and the formed Ce(TRIPCO2)5Na was combined to obtain brown-red crystals (4.36 g, total yield of 62%).

[0047] Example 1: Preparation of 1-cyclohexyl-3,5-dimethyl-1H-pyrazole by one-pot three-step method under cerium-free catalytic light irradiation conditions (this example 1 is a comparative example)

[0048] The chemical reaction formula for preparing the compound 1-cyclohexyl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0049]

[0050] The specific process is as follows:

[0051] A stirring bar, cyclohexylmethanol (22.8 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle in sequence. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (L max=400nm, 2.5W) was irradiated for 18h. After the reaction was completed, the solvent was removed by distillation under reduced pressure. Subsequently, 2mL of methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 1-cyclohexyl-3,5-dimethyl-1H-pyrazole was not generated (the yield was 0%).

[0052] Example 2: One-pot three-step preparation of 1-cyclohexyl-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0053] The chemical reaction formula for preparing the compound 1-cyclohexyl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0054]

[0055] The specific process is as follows:

[0056] A stirring bar, cyclohexylmethanol (22.8 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle in sequence. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed in a LEDs (L max =400nm, 2.5W) was irradiated for 18h. After the reaction was completed, the solvent was removed by distillation under reduced pressure. Subsequently, 2mL of methanol solution of hydrochloric acid (4mol / L) was added to the reaction bottle, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction bottle under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 1-cyclohexyl-3,5-dimethyl-1H-pyrazole was obviously generated.

[0057] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (24.9 mg, 70%) was obtained by column chromatography (petroleum ether / ethyl acetate = 20:1).

[0058] The structural data of the product prepared in this example are characterized as follows:

[0059] 1 H NMR (400MHz, CDCl3) δ5.74(s,1H),3.91-3.79(m,1H),2.21(s,3H),2.20(s,3H),1.99-1.78(m,6H),1.71-1.64(m,1H),1.42-1.23(m,3H). 13 C NMR(100MHz, CDCl3)δ146.9,137.7,104.6,57.2,33.0,26.0,25.3,13.8,11.2.HRMS(EI+):calcd.for C11H18N2 + ([M] + )178.1465, found 178.1466.

[0060] Example 3: Preparation of 1-cycloheptyl-3,5-dimethyl-1H-pyrazole by one-pot three-step method under photocatalytic conditions of cerium

[0061] The chemical reaction formula for preparing the compound 1-cycloheptyl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0062]

[0063] The specific process is as follows:

[0064] A stirring bar, cycloheptylmethanol (25.6 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under the LEDs (λ max =400nm, 2.5W) irradiation for 18h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, 2mL HCl (4M in MeOH) solution is added to the reaction bottle, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in vacuo. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction bottle under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-cycloheptyl-3,5-dimethyl-1H-pyrazole is obviously generated.

[0065] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (31.1 mg, 81%) was obtained by column chromatography (petroleum ether / ethyl acetate = 20:1).

[0066] The structural data of the product prepared in this example are characterized as follows:

[0067] 1 H NMR(400MHz, CDCl3)δ5.75(s,1H),4.13–4.03(m,1H),2.23(s,3H),2.22(s,3H),2.16–2 .02(m,2H),1.97–1.88(m,2H),1.87–1.78(m,2H),1.69–1.59(m,4H),1.55–1.44(m,2H). 13 C NMR(100MHz, CDCl3)δ146.8,137.3,104.5,59.8,35.0,27.7,25.1,13.8,11.2.HRMS(EI+):calcd.for C 12 H 20 N2 + ([M] + )192.1621, found 192.1625.

[0068] Example 4: Preparation of 1-methylcyclohexyl-3,5-dimethyl-1H-pyrazole by one-pot three-step method under cerium catalysis

[0069] The chemical reaction formula for preparing the compound 1-methylcyclohexyl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0070]

[0071] The specific process is as follows:

[0072] A stirring bar, (1-methylcyclohexyl)methanol (25.6 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle in sequence. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max=400nm, 2.5W) irradiation for 18h. After the reaction was completed, the solvent was removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 1-methylcyclohexyl-3,5-dimethyl-1H-pyrazole was clearly generated.

[0073] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (31.5 mg, 82%) was obtained by column chromatography (petroleum ether / ethyl acetate = 20:1).

[0074] The structural data of the product prepared in this example are characterized as follows:

[0075] 1 H NMR(400MHz, CDCl3)δ5.78(s,1H),2.47–2.39(m,2H),2.36(s,3H),2.21(s, 3H),1.80–1.71(m,2H),1.64–1.52(m,4H),1.49–1.43(m,2H),1.40(s,3H). 13 C NMR(100MHz, CDCl3)δ145.3,138.6,107.9,62.0,37.6,27.1,25.7,22.6,15.0,13.6.HRMS(EI+):calcd.for C 12 H 20 N2 + ([M] + )192.1621, found 192.1623.

[0076] Example 5: One-pot three-step preparation of 1-(3-cyclohexenyl)-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0077] The chemical reaction formula for preparing the compound 1-(3-cyclohexenyl)-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0078]

[0079] The specific process is as follows:

[0080] A stirring bar, 3-cyclohexenylmethanol (22.4 mg, 25.6 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 18h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) is added to the reaction flask, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction flask under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-(3-cyclohexenyl)-3,5-dimethyl-1H-pyrazole is clearly generated.

[0081] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (15.5 mg, 44%) was obtained by column chromatography (petroleum ether / ethyl acetate = 20:1).

[0082] The structural data of the product prepared in this example are characterized as follows:

[0083] 1 H NMR(400MHz, CDCl3)δ5.77(s,1H),5.75–5.66(m,2H),4.23–4.08(m,1H),2.74-2.62(m,1H),2 .31–2.26(m,1H),2.26–2.24(m,2H),2.24–2.22(m,6H),2.21–2.15(m,1H),1.97–1.89(m,1H). 13 C NMR(100MHz, CDCl3)δ147.2,138.1,126.6,125.2,104.8,53.8,31.9,29.1,25.8,13.8,11.2.HRMS(EI+):calcd.for C 11 H 16 N2 + ([M] + )176.1308, found 176.1304.

[0084] Example 6: One-pot three-step preparation of 1-bicyclo[2.2.1]hept-2-yl-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0085] The chemical reaction formula for preparing the compound 1-bicyclo[2.2.1]hept-2-yl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0086]

[0087] The specific process is as follows:

[0088] A stirring bar, bicyclo[2.2.1]hept-2-ylmethanol (25.2 mg, 0.2 mmol), DBAD (230 mg, 1.0 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) is added to the reaction flask, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction flask under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-bicyclo[2.2.1]hept-2-yl-3,5-dimethyl-1H-pyrazole is clearly generated.

[0089] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (24.7 mg, 65%) was obtained by column chromatography (petroleum ether / ethyl acetate = 20:1).

[0090] The structural data of the product prepared in this example are characterized as follows:

[0091] 1 H NMR(400MHz, CDCl3)δ5.80(s,1H),3.97(dd,J=8.4,4.2Hz,1H),2.45–2.40(m,1H),2.37–2.31(m ,2H),2.23(s,6H),2.09–2.02(m,1H),1.78–1.70(m,1H),1.64–1.50(m,2H),1.30–1.16(m,3H).13 C NMR(100MHz, CDCl3)δ146.2,138.8,105.4,60.8,43.4,37.7,36.0,35.8,28.7,27.6,13.7,11.5.HRMS(EI+):calcd.for C 12 H 18 N2 + ([M] + )190.1465,found190.1468.

[0092] Example 7: Preparation of 3-(3,5-dimethyl-1H-pyrazol-1-yl)-adamantan-1-ol by one-pot three-step method under photocatalytic conditions

[0093] The chemical reaction formula for preparing the compound 3-(3,5-dimethyl-1H-pyrazol-1-yl)-adamantan-1-ol in this example is as follows:

[0094]

[0095] The specific process is as follows:

[0096] A stirring bar, 3-hydroxy-1-adamantanemethanol (36.4 mg, 0.2 mmol), DBAD (230 mg, 1.0 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction, the solvent was removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 3-(3,5-dimethyl-1H-pyrazol-1-yl)-adamantan-1-ol was clearly generated.

[0097] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled off the solvent under reduced pressure to obtain a crude product. A white solid (14.8 mg, 30%) was obtained by column chromatography (petroleum ether / ethyl acetate = 5:1).

[0098] The structural data of the product prepared in this example are characterized as follows:

[0099] 1 H NMR(400MHz, CDCl3)δ5.78(s,1H),2.44–2.39(m,3H),2.39–2.34(m,2H),2 .27–2.23(m,2H),2.22–2.10(m,7H),1.79–1.69(m,4H),1.66–1.53(m,2H). 13 C NMR(100MHz, CDCl3)δ145.6,138.6,108.2,69.7,62.6,49.8,44.0,41.0,34.8,31.0,15.0,13.5.HRMS(EI+):calcd.for C 15 H 22 ON2 + ([M] + )246.1727, found246.1730.

[0100] Example 8: One-pot three-step preparation of 1-benzyl-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0101] The chemical reaction formula for preparing the compound 1-benzyl-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0102]

[0103] The specific process is as follows:

[0104] A stirring bar, phenylethanol (24.2 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle in sequence. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction was completed, the solvent was removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 1-benzyl-3,5-dimethyl-1H-pyrazole was clearly generated.

[0105] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (22.3 mg, 60%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0106] The structural data of the product prepared in this example are characterized as follows:

[0107] 1 H NMR (400MHz, CDCl3) δ7.36–7.17(m,3H),7.14–6.98(m,2H),5.85(s,1H),5.21(s,2H),2.25(s,3H),2.14(s,3H) 13 C NMR(100MHz, CDCl3)δ147.6,139.3,137.4,128.7,127.5,126.6,105.6,52.6,13.6,11.2.HRMS(EI+):calcd.for C 12 H 14 N2 + ([M] + )186.1152, found 186.1151.

[0108] Example 9: One-pot three-step preparation of 1-(4-bromobenzyl)-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0109] The chemical reaction formula for preparing the compound 1-(4-bromobenzyl)-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0110]

[0111] The specific process is as follows:

[0112] A stirring bar, 4-bromophenethanol (40.2 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle in sequence. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max=400nm, 2.5W) irradiation for 24h. After the reaction was completed, the solvent was distilled off under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 1-(4-bromobenzyl)-3,5-dimethyl-1H-pyrazole was clearly generated.

[0113] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (39.1 mg, 74%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0114] The structural data of the product prepared in this example are characterized as follows:

[0115] 1 H NMR (400MHz, CDCl3) δ7.50–7.35(m,2H),6.98–6.82(m,2H),5.84(s,1H),5.14(s,2H),2.23(s,3H),2.12(s,3H). 13 C NMR(100MHz, CDCl3)δ148.0,139.3,136.7,131.9,128.4,121.5,105.9,52.1,13.6,11.3.HRMS(FI+):calcd.for C 12 H 13 N2Br + ([M] + )264.0257, found 264.0262.

[0116] Example 10: Preparation of methyl 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzoate by one-pot three-step method under photocatalytic conditions

[0117] The chemical reaction formula for preparing the compound 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzoic acid methyl ester in this example is as follows:

[0118]

[0119] The specific process is as follows:

[0120] A stirring bar, methyl 4-(2-hydroxyethyl)benzoate (38.8 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction was completed, the solvent was removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) was added to the reaction flask, and the mixture was heated at 40°C for 3 hours. After the reaction was completed, the mixture was concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) were added to the reaction flask under a nitrogen atmosphere, and the mixture continued to react at 40°C for 3 hours. The reaction was stopped and monitored by thin layer chromatography. The product 4-[(3,5-dimethyl-1H-pyrazol-1-yl)methyl]benzoic acid methyl ester was obviously generated.

[0121] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (28.8 mg, 59%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0122] The structural data of the product prepared in this example are characterized as follows:

[0123] 1 H NMR (400MHz, CDCl3) δ8.01–7.86(m,2H),7.14–7.01(m,2H),5.86(s,1H),5.25(s,2H),3.88(s,3H),2.24(s,3H),2.12(s,3H). 13 C NMR(100MHz, CDCl3)δ166.8,148.0,142.6,139.4,130.1,129.4,126.5,105.8,52.3,52.2,13.6,11.1.HRMS(EI+):calcd.forC 14 H 16 N2O2 + ([M] + )244.1206, found 244.1211.

[0124] Example 11: One-pot three-step preparation of 1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)-1H-pyrazole under photocatalytic conditions

[0125] The chemical reaction formula for preparing the compound 1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)-1H-pyrazole in this example is as follows:

[0126]

[0127] The specific process is as follows:

[0128] A stirring bar, 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)ethanol (57.6 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) is added to the reaction flask, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction flask under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)-1H-pyrazole is clearly generated.

[0129] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (39.3 mg, 63%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0130] The structural data of the product prepared in this example are characterized as follows:

[0131] 1H NMR (500MHz, CDCl3) δ7.74(d,J=8.0Hz,2H),7.08(d,J=8.0Hz,2H),5.85(s,1H),5.24(s,2H),2.25(s,3H),2.11(s,3H),1.32(s,12H). 13 C NMR (126MHz, CDCl3) δ147.6,140.5,139.4,135.3,126.0,105.7,83.9,52.9,24.9,13.6,11.2.Asignal for the carbon directly attached to the boron atom was not observed.HRMS(DART+):calcd.forC 18 H 26 N2O2 10 B + ([M+H] + )312.2118, found 312.2118.

[0132] Example 13: One-pot three-step preparation of 1-(benzofuran-5-ylmethyl)-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0133] The chemical reaction formula for preparing the compound 1-(benzofuran-5-ylmethyl)-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0134]

[0135] The specific process is as follows:

[0136] A stirring bar, 2-(benzofuran-5-yl)ethanol (32.4 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under the LEDs (λ max=400nm, 2.5W) irradiation for 24h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) is added to the reaction flask, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction flask under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-(benzofuran-5-ylmethyl)-3,5-dimethyl-1H-pyrazole is clearly generated.

[0137] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (22.6 mg, 50%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0138] The structural data of the product prepared in this example are characterized as follows:

[0139] 1 H NMR (400MHz, CDCl3) δ7.59(s,1H),7.50–7.37(m,1H),7.29(s,1H),7.13–7. 00(m,1H),6.70(s,1H),5.86(s,1H),5.30(s,2H),2.27(s,3H),2.16(s,3H). 13 C NMR (100MHz, CDCl3) δ154.4,147.6,145.6,139.2,132.0,127.8,123.2,119.4,111.6,106.7,105.7,52.8,13.6,11.3.HRMS(EI+):calcd.for C 14 H 14 N2O + [(M) + ]226.1101, found 226.1105.

[0140] Example 13: One-pot three-step preparation of 1-(benzo[b]thiophen-3-ylmethyl)-3,5-dimethyl-1H-pyrazole under photocatalytic conditions

[0141] The chemical reaction formula for preparing the compound 1-(benzo[b]thiophen-3-ylmethyl)-3,5-dimethyl-1H-pyrazole in this example is as follows:

[0142]

[0143] The specific process is as follows:

[0144] A stirring bar, 2-(benzo[b]thiophene-3-yl)ethanol (35.6 mg, 0.2 mmol), DBAD (69.0 mg, 0.3 mmol), Ce(TRIPCO2)5Na (16.8 mg, 12 μmol), and MeCN (2 mL, 0.1 M) were added to a dried 8 mL reaction bottle. The lid was tightened with a polytetrafluoroethylene gasket, and the reaction mixture was bubbled with argon for 10 minutes, then sealed with a sealing film and placed under LEDs (λ max =400nm, 2.5W) irradiation for 24h. After the reaction is completed, the solvent is removed by distillation under reduced pressure. Subsequently, a methanol solution of hydrochloric acid (4mol / L) is added to the reaction flask, and the mixture is heated at 40°C for 3 hours. After the reaction is completed, the mixture is concentrated in a vacuum. Subsequently, acetylacetone (60.0mg, 0.6mmol), triethylamine (20.2mg, 0.2mmol) and MeOH (0.5mL, 0.4M) are added to the reaction flask under a nitrogen atmosphere, and the mixture continues to react at 40°C for 3 hours. The reaction is stopped and monitored by thin layer chromatography. The product 1-(benzo[b]thiophen-3-ylmethyl)-3,5-dimethyl-1H-pyrazole is clearly generated.

[0145] The mixture was extracted with water and ethyl acetate (10 mL x 2 times). The organic phases were combined, dried over anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product. A yellow oily liquid (20.3 mg, 42%) was obtained by column chromatography (petroleum ether / ethyl acetate = 10:1).

[0146] The structural data of the product prepared in this example are characterized as follows:

[0147] 1 H NMR (400MHz, CDCl3) δ7.82–7.63(m,2H),7.36–7.21(m,2H),7.05(s,1H),5.85(s,1H),5.42(s,2H),2.25(s,6H). 13 C NMR (100MHz, CDCl3) δ148.2,140.7,139.9,139.5,139.3,124.5,124.4,123.6,122.4,122.0,106.0,48.6,13.7,11.2.HRMS(EI+):calcd.forC 14 H 14 N2S + ([M] + )242.0872, found 242.0877.

[0148] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0149] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds, characterized in that The reaction formula is as follows:

2. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 1, characterized in that The following steps are involved: The first step is to remove the hydroxymethyl group by hydrazine reaction. Alkyl methanol and di-tert-butyl azodicarboxylate are used as raw materials, cerium catalyst and organic solvent are added, stirred evenly, and reacted for a certain period of time under light conditions to obtain the precursor of N-alkyl substituted 3,5-dimethylpyrazole; Step 2: Boc deprotection, spin dry the reaction system obtained in the first step, add hydrochloric acid methanol solution to react; Step 3: Knorr heterocyclic condensation, the reaction system obtained in the second step is dried by rotation, acetylacetone, triethylamine and methanol are added to react to obtain N-alkyl substituted 3,5-dimethylpyrazole compounds.

3. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 2, characterized in that: The organic solvent for the first step reaction is any one of acetonitrile, benzonitrile, chlorobenzene, trifluorotoluene, N,N-dimethylformamide, acetone and dichloromethane; the cerium catalyst is a sodium cerium pentatriisopropylbenzoate complex; the alkylmethanol includes but is not limited to cyclohexylmethanol, cycloheptylmethanol, 1-(methylcyclohexyl)methanol, 3-cyclohexene-1-methanol, bicyclo[2.2.1]hept-2-ylmethanol, 3-hydroxy-1-adamantanemethanol, phenylethanol, 4-bromophenylethanol, 4-(2-hydroxyethyl)benzoic acid methyl ester, 2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)ethanol, 2-(benzofuran-5-yl)ethanol, and 2-(benzo[b]thiophene-3-yl)ethanol.

4. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 2, characterized in that: The molar ratio of alkylmethanol to di-tert-butyl azodicarboxylate is 1:1.0-5.0; the molar ratio of alkylmethanol to cerium catalyst is 1:0.01-0.06; the ratio of the amount of alkylmethanol in millimole to the volume of the organic solvent in milliliters is 1:5.0-25.

0.

5. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 2, characterized in that: The light source in the first step of the illumination condition is visible light; the reaction time under the illumination condition is 6-24 hours.

6. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 2, characterized in that: In the second step, the concentration of the hydrochloric acid methanol solution is 4 mol / L, and its dosage is 40 times the equivalent of the alkyl methanol; the reaction temperature is 40° C., and the reaction time is 3 hours.

7. The one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to claim 2, characterized in that: In the third step, the amount of acetylacetone used is 3 times the equivalent of the alkyl methanol; the amount of triethylamine used is 1 times the equivalent of the alkyl methanol; the reaction temperature is 40° C., and the reaction time is 3 hours.

8. A one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds according to any one of claims 1 to 7, characterized in that: The method also includes a fourth step, namely a separation and purification step.

9. A one-pot method for synthesizing N-alkyl-substituted 3,5-dimethylpyrazole compounds as claimed in claim 8, characterized in that: The specific operation of the separation and purification step is: after the reaction in the third step is completed, the mixture is extracted once with water and ethyl acetate respectively; the organic phases are combined, dried with anhydrous Na2SO4, and further distilled under reduced pressure to remove the solvent to obtain a crude product; the crude product is then separated by column chromatography to obtain N-alkyl substituted 3,5-dimethylpyrazole compounds.

10. N-alkyl substituted 3,5-dimethylpyrazole compounds prepared by the method according to claim 9.

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